Brian Yates

Computational Study of Intramolecular Arene Palladation at a Palladium(IV) Center

Publisher: American Chemical Society (ACS)

Date: 04-03-2015

DOI: 10.1021/OM5013049

Basicity of Nucleophilic Carbenes in Aqueous and Nonaqueous Solvents - Theoretical Predictions

Publisher: American Chemical Society (ACS)

Date: 22-06-2004

DOI: 10.1021/JA038973X

Abstract: The complete basis set method CBS-QB3 was used in conjunction with the CPCM solvation model to predict both the absolute and relative pKa's of 12 nucleophilic carbenes in dimethyl sulfoxide (DMSO), acetonitrile (MeCN), and water. Average absolute pKa values in DMSO ranged from 14.4 +/- 0.16 for 3-methylthiazol-2-ylidene (12) to 27.9 +/- 0.23 in the case of bis(dimethylamino)carbene (11), while values in MeCN were determined to be between 25.7 +/- 0.16 (12) and 39.1 +/- 0.25 (11). Relative pKa calculations yielded similar results. Calculations in aqueous solution gave pKa's between 21.2 +/- 0.2 (12) and 34.0 +/- 0.3 (11). Excellent agreement between calculated and experimental pKa's was obtained for the few cases where experimental numbers are available, confirming that this theoretical approach may be used to calculate highly accurate pKa values.

DFT Studies on the Carboxylation of the C–H Bond of Heteroarenes by Copper(I) Complexes

Publisher: American Chemical Society (ACS)

Date: 31-10-2011

DOI: 10.1021/OM200744A

A Modified Cationic Mechanism for PdCl₂-Catalyzed Transformation of a Homoallylic Alcohol to an Allyl Ether

Publisher: American Chemical Society (ACS)

Date: 31-07-2019

DOI: 10.1021/ACS.ORGANOMET.9B00276

Ligand effects in bimetallic high oxidation state palladium systems

Publisher: American Chemical Society (ACS)

Date: 02-11-2010

DOI: 10.1021/IC1020912

Abstract: Ligand effects in bimetallic high oxidation state systems containing a X-Pd-Pd-Y framework have been explored with density functional theory (DFT). The ligand X has a strong effect on the dissociation reaction of Y to form [X-Pd-Pd](+) + Y(-). In the model system examined where Y is a weak σ-donor ligand and a good leaving group, we find that dissociation of Y is facilitated by greater σ-donor character of X relative to Y. We find that there is a linear correlation of the Pd-Y and Pd-Pd bond lengths with Pd-Y bond dissociation energy, and with the σ-donating ability of X. These results can be explained by the observation that the Pd d(z(2)) population in the PdY fragment increases as the donor ability of X increases. In these systems, the Pd(III)-Pd(III) arrangement is favored when X is a weak σ-donor ligand, while the Pd(IV)-Pd(II) arrangement is favored when X is a strong σ-donor ligand. Finally, we demonstrate that ligand exchange to form a bimetallic cationic species in which each Pd is six-coordinate should be feasible in a high polarity solvent.

Cover Picture: Dual Gold‐Catalyzed Cycloaromatization of Unconjugated (E)‐Enediynes (Angew. Chem. Int. Ed. 7/2019)

Publisher: Wiley

Date: 21-12-2019

DOI: 10.1002/ANIE.201814227

Reduction of a platinum(iv) prodrug model by sulfur containing biological reductants: computational mechanistic elucidation

Publisher: Royal Society of Chemistry (RSC)

Date: 2018

DOI: 10.1039/C8CC05682J

Abstract: In order for the usual l -Cys zwitterion to reduce Pt IV , it is first required to tautomerise into its unusual form.

A Comparison of N₂ Cleavage in Schrock's Mo[N₃N] and Laplaza–Cummins' Mo[N(R)Ar]₃ Systems

Publisher: Wiley

Date: 29-12-2008

DOI: 10.1002/CHEM.200801127

Abstract: The four-coordinate Mo[N(3)N] complex, [N(3)N] = [{RNCH(2)CH(2)}(3)N], R = 3,5-(2,4,6-iPr(3)C(6)H(2))(2)C(6)H(3) (HIPT), which is capable of converting N(2) to ammonia catalytically, reacts with N(2) in a similar manner to Mo[N(R)Ar](3) (R = tBu, Ar = 3,5-C(6)H(3)Me(2)) to form a dinitrogen-bridged dimer intermediate, but unlike its three-coordinate counterpart, N(2) cleavage is not observed. To rationalise these differences, the reaction of N(2) with the model Mo[NH(2)](3)[NH(3)] and full ligand Mo[N(3)N] systems was explored using density functional theory and compared with the results of an earlier study involving the model three-coordinate Mo[NH(2)](3) system. Although the overall reaction is exothermic, the final N-N cleavage step is calculated to be endothermic by 75 kJ mol(-1) for the model system when the Mo-amine cap bond length is fixed to mimic the constraints of the ligand straps, but exothermic by 14 kJ mol(-1) for the full ligand system. In the latter case, the slightly exothermic cleavage step can be attributed to the destabilization of the N(2) bridged dimer relative to the nitride product owing to the steric effects of the bulky R groups. The activation barrier for N-N cleavage is estimated at 151 kJ mol(-1) for the model system, more than twice the calculated value for Mo[NH(2)](3), and even greater, 213 kJ mol(-1), for the full ligand [N(3)N]Mo system. A bonding analysis shows that although the binding of the amine cap helps to stabilize the intermediate dimer, at the same time it destabilizes the metal d-orbitals involved in backbonding to the pi* orbitals on N(2). As a result, backdonation is less efficient and N-N activation reduced compared to the three-coordinate system. Thus, the increased stability of the intermediate dimer on binding of the amine cap combined with the reduced level of N-N activation and higher kinetic barrier, explain why N-N cleavage has not been observed experimentally for the four-coordinate Mo[N(3)N] system.

Organoactinides Promote the Dimerization of Aldehydes: Scope, Kinetics, Thermodynamics, and Calculation Studies

Publisher: American Chemical Society (ACS)

Date: 11-01-2011

DOI: 10.1021/JA105696P

Abstract: Surprising catalytic activities have been found for the actinide complexes Cp*(2)ThMe(2) (1), Th(NEtMe)(4) (2), and Me(2)SiCp''(2)Th(C(4)H(9))(2) (3) toward oxygenated substrates. During the catalytic dimerization of benzaldehydes to their corresponding esters, complexes 1 and 2 gave 65 and 85% yield in 48 h, respectively, while the geometry-constrained complex 3 gave 96% yield in 24 h. Exploring the effect of substituents on benzaldehyde, it has been found that, in general, electron-withdrawing groups facilitate the reaction. Kinetic study with complexes 1 and 3 reveals that the rate of the reaction is first order in catalyst and substrate, which suggests the rate equation "rate = k[catalyst](1)[aldehyde](1)". The activation energy of the reaction was found to be 7.16 ± 0.40 and 3.47 ± 0.40 kcal/mol for complexes 1 and 3 respectively, which clearly indicates the advantage of the geometry-constrained complex. Astonishing are the reactivity of the organoactinide complexes with oxygen-containing substrates, and especially the reactivity of complex 3, toward the dimerization of substrates like p-methoxybenzaldehyde, m -nitrobenzaldehyde, and furanaldehyde and the reactivity toward the polymerization of terephthalaldehyde. Density functional theory mechanistic study reveals that the catalytic cycle proceeds via an initially four-centered transition state (+6 kcal/mol), followed by the rate-determining six-centered transition state (+13.5 kcal/mol), to yield thermodynamically stable products.

Buckling under strain: Relief of steric pressure occurs differently for samarium(III) porphyrinogen complexes of the π-bound auxiliary ligands cyclopentadienyl and cyclooctatetraenediyl

Publisher: American Chemical Society (ACS)

Date: 16-02-2007

DOI: 10.1021/OM061143I

Sulfur Dioxide Activation: A Theoretical Investigation into Dual S═O Bond Cleavage by Three-Coordinate Molybdenum(III) Complexes

Publisher: American Chemical Society (ACS)

Date: 05-01-2015

DOI: 10.1021/IC502298J

Abstract: Cummins et al. have observed that 3 equiv of Mo(N[R]Ar)3 (R = C(CD3)2CH3, Ar = 3,5-C6H3Me2) are required for dual S═O bond cleavage within a SO2 molecule. Using density functional theory calculations, this theoretical study investigates a mechanism for this SO2 cleavage reaction that is mediated by MoL3, where L = NH2 or N[(t)Bu]Ph. Our results indicate that an electron transfers into the SO2 ligand, which leads to Mo oxidation and initiates SO2 coordination along the quartet surface. The antiferromagnetic (AF) nature of the (NH2)3Mo-SO2 adduct accelerates intersystem crossing onto the doublet surface. The first S═O bond cleavage occurs from the resulting doublet adduct and leads to formation of L3Mo═O and SO. Afterward, the released SO molecule is cleaved by the two remaining MoL3, resulting in formation of L3Mo═S and an additional L3Mo═O. This mononuclear mechanism is calculated to be strongly exothermic and proceeds via a small activation barrier, which is in accordance with experimental results. An additional investigation into a binuclear process for this SO2 cleavage reaction was also evaluated. Our results show that the binuclear mechanism is less favorable than that of the mononuclear mechanism.

Achieving C–N bond cleavage in dinuclear metal cyanide complexes

Publisher: Royal Society of Chemistry (RSC)

Date: 2011

DOI: 10.1039/C1DT10225G

Abstract: Cleavage of cyanide is more difficult to achieve compared to dinitrogen and carbon monoxide, even though these species contain triple bonds of greater strength. In this work, we have used computational methods to investigate thermodynamic and mechanistic aspects of the C-N bond cleavage process in [L(3)M-CN-M'L(3)] systems consisting of a central cyanide unit bound in an end-on fashion to two terminal metal tris-amide complexes. In these systems, [M] is a d(3) transition metal from the 3d, 4d, 5d, or 6d series and groups 4 through 7, and [L] is either [NH(2)], [NMe(2)], [N(i)PrPh], or [N(t)BuAr]. A comparison of various models for the experimentally relevant [L(3)Mo-CN-MoL(3)] system has shown that while the C-N cleavage step appears to be an energetically favourable process, a large barrier exists for the dissociation of [L(3)Mo-CN-MoL(3)]((-)) into [L(3)Mo-C]((-)) and [N-MoL(3)], which possibly explains why C-N bond scission is not observed experimentally. The general structural, bonding, and thermochemical trends across the transition metal series investigated, indicate that the systems exhibiting the greatest degree of C-N activation, and most favourable energetics for C-N cleavage, also possess the most favourable electronic properties, namely, a close match between the relevant π-like orbitals on the metal-based and cyanide fragments. The negative charge on the cyanide fragment leads to significant destabilization of the π* level which needs to be populated through back-donation from the metal centres in order for C-N bond scission to be achieved. Therefore, metal-based systems with high-lying d(π) orbitals are best suited to C-N cleavage. In terms of chemical periodicity, these systems can be identified as the heavier members within a group and the earlier members within a period. As a consequence, Mo complexes are not well suited to cleaving the C-N bond, whereas the Ta analogues are the most favourable systems and should, in principle, be capable of cleaving cyanide under relatively mild conditions. An important conclusion from this work is that a successful strategy for achieving cleavage of multiply-bonded, and relatively unreactive, molecular fragments, may simply lie in tuning the electronic structures and orbital interactions by judicious choice of metal sites and ligand groups.

A Computational Mechanistic Investigation into Reduction of Gold(III) Complexes by Amino Acid Glycine: A New Variant for Amine Oxidation

Publisher: Wiley

Date: 16-05-2018

DOI: 10.1002/CHEM.201800403

Abstract: Density functional theory (DFT) was utilized to explore the reduction of gold(III) complexes by the amino acid glycine (Gly). Interestingly, when the nitrogen atom of Gly coordinates to the gold(III) center, its C

Nucleophilic acyl substitution of acyl diimides

Publisher: American Chemical Society (ACS)

Date: 16-06-2009

DOI: 10.1021/JO900923M

Abstract: The nucleophilic acyl substitution of the acyl diimide intermediate formed by the oxidation of isoniazid was found to involve two methanol molecules in a six-membered cyclic transition state. Calculations were performed in the gas phase at the B3LYP/6-311+G(d,p)//B3LYP/6-31G(d) level of theory and solvation effects were included both explicitly and implicitly by using CPCM. The effect of electron withdrawing and donating groups on the aryl ring was also explored. The results obtained are in good agreement with experimental observations for the oxidation of isoniazid.

Computational Organic Chemistry

Publisher: Royal Society of Chemistry (RSC)

Date: 2002

DOI: 10.1039/B110351M

Nature of the metal-alkene bond in platinum complexes of strained olefins

Publisher: American Chemical Society (ACS)

Date: 20-01-1999

DOI: 10.1021/OM9805842

Computational study of C(sp³)–O bond formation at a Pd^IV centre

Publisher: Royal Society of Chemistry (RSC)

Date: 2017

DOI: 10.1039/C7DT00096K

Abstract: This report describes a computational study of C(sp 3 )–OR bond formation from Pd IV complexes of general structure Pd IV (CH 2 CMe 2 - o -C 6 H 4 - C , C ′)(F)(OR)(bpy- N , N ′) (bpy = 2,2′-bipyridine).

The Mechanism of the Stetter Reaction – A DFT Study

Publisher: Wiley

Date: 11-2008

DOI: 10.1002/EJOC.200800506

Experimental and computational study of a reductive elimination mechanism in a methyl-Pd(II)-CNC carbene complex

Publisher: Royal Society of Chemistry (RSC)

Date: 2002

DOI: 10.1039/B207020K

Chemical Kinetics of a Bipalladium Complex

Publisher: American Chemical Society (ACS)

Date: 10-01-2013

DOI: 10.1021/JP310368G

Abstract: A theoretical model is presented, for reductive elimination in a bipalladium complex, based on the model of Ariafard et al. (2011). This reaction is of particular interest due to the novel Pd(III) intermediate. A thermo-kinetic model is proposed for this reaction scheme, and the rate laws and energy balance are given as a system of ordinary differential equations. A simplified model is then derived that only involves two key variables, so that the system can be analyzed completely in a phase plane. It is shown that kinetic oscillations do not occur, but that there are multiple steady states for the reaction. These new features are confirmed by a numerical analysis of the full model scheme. The predictions provide a mechanism to test the model and the underlying computational chemistry.

Gold‐Catalyzed Regiospecific Annulation of Unsymmetrically Substituted 1,5‐Diynes for the Precise Synthesis of Bispentalenes

Publisher: Wiley

Date: 28-08-2019

DOI: 10.1002/CHEM.201902381

Tris(pentafluorphenyl)boran‐katalysierte Erzeugung von Carbenium‐Ionen und autokatalytische Pyrazol‐Synthese – eine theoretische und experimentelle Studie

Publisher: Wiley

Date: 12-10-2021

DOI: 10.1002/ANGE.202109744

Abstract: In den letzten Jahren hat sich die metallfreie organische Synthese unter Verwendung von Triarylboranen als Katalysatoren zu einem weit verbreiteten Forschungsgebiet entwickelt. Hier berichten wir über eine umfassende theoretische und experimentelle Studie für die hochselektive Synthese von N‐substituierten Pyrazolen durch die Erzeugung von Carbenium‐Ionen aus der Reaktion zwischen Arylestern und Vinyldiazoacetaten in Gegenwart von katalytischem Tris(pentafluorphenyl)boran [B(C 6 F 5 ) 3 ]. DFT‐Studien zum Reaktionsmechanismus zeigen, dass die In‐situ‐Generierung einer Carbenium‐Spezies als Autokatalysator fungiert, welcher die regiospezifische Bildung von N‐substituierten Pyrazolen in guter bis hervorragender Ausbeute (bis zu 81 %) auslöst.

Rhodium-Catalyzed C−C Coupling Reactions: Mechanistic Considerations

Publisher: American Chemical Society (ACS)

Date: 23-08-2008

DOI: 10.1021/OM800472V

Titanium-mediated rearrangement of cyclopropenylmethyl acetates to (E)-halodienes

Publisher: Royal Society of Chemistry (RSC)

Date: 2011

DOI: 10.1039/C0OB01046D

Abstract: TiCl(4) and TiBr(4) rapidly transform cyclopropenylmethyl acetates to (E)-halodienes via ring-opening to allyl-vinyl cations. DFT calculations suggest that the regioselectivity of the halogenation of this cationic intermediate by [TiX(4)OAc](-) is under thermodynamic control, while the stereoselectivity is governed by kinetics.

Lewis Acidic Behavior of Fluorinated Organomercurials

Publisher: American Chemical Society (ACS)

Date: 29-09-2007

DOI: 10.1021/OM070125D

Ligand rotation in [Ar(R)N](3)M-N-2-M '[N(R)Ar](3) (M, M ' = Mo-III, Nb-III; R = Pr-i and Bu-t) dimers

Publisher: Royal Society of Chemistry (RSC)

Date: 2005

DOI: 10.1039/B413766C

Abstract: Earlier calculations on the model N2-bridged dimer (micro-N2)-{Mo[NH2]3}2 revealed that ligand rotation away from a trigonal arrangement around the metal centres was energetically favourable resulting in a reversal of the singlet and triplet energies such that the singlet state was stabilized 13 kJ mol(-1) below the D(3d) triplet structure. These calculations, however, ignored the steric bulk of the amide ligands N(R)Ar (R =iPr and tBu, Ar = 3,5-C6H3Me2) which may prevent or limit the extent of ligand rotation. In order to investigate the consequences of steric crowding, density functional calculations using QM/MM techniques have been performed on the Mo(III)Mo(III) and Mo(III)Nb(III) intermediate dimer complexes (mu-N(2))-{Mo[N(R)Ar]3}2 and [Ar(R)N]3Mo-(mu-N2)-Nb[N(R)Ar]3 formed when three-coordinate Mo[N(R)Ar]3 and Nb[N(R)Ar]3 react with dinitrogen. The calculations indicate that ligand rotation away from a trigonal arrangement is energetically favourable for all of the ligands investigated and that the distortion is largely electronic in origin. However, the steric constraints of the bulky amide groups do play a role in determining the final orientation of the ligands, in particular, whether the ligands are rotated at one or both metal centres of the dimer. Analogous to the model system, QM/MM calculations predict a singlet ground state for the (mu-N2)-{Mo[N(R)Ar]3}2 dimers, a result which is seemingly at odds with the experimental triplet ground state found for the related (mu-N2)-{Mo[N(tBu)Ph]3}2 system. However, QM/MM calculations on the (mu-N2)-{Mo[N(tBu)Ph]3}2 dimer reveal that the singlet-triplet gap is nearly 20 kJ mol(-1) smaller and therefore this complex is expected to exhibit very different magnetic behaviour to the (mu-N2)-{Mo[N(R)Ar]3}2 system.

Total Synthesis of (±)-Dihydroisosubamol

Publisher: Wiley

Date: 23-12-2016

DOI: 10.1002/ADSC.201600663

Disclosure of Some Obscure Mechanistic Aspects of the Copper-Catalyzed Click Reactions Involving N₂ Elimination Promoted by the Use of Electron-Deficient Azides from a DFT Perspective

Publisher: American Chemical Society (ACS)

Date: 26-12-2018

DOI: 10.1021/ACS.ORGANOMET.8B00691

Theoretical Investigation into the Mechanism of Ethylene Polymerization by a Cationic Dinuclear Aluminum Complex: A Longstanding Unresolved Issue

Publisher: American Chemical Society (ACS)

Date: 28-02-2013

DOI: 10.1021/OM3011239

Synthesis, structure and optical limiting properties of organoruthenium-chalcogenide clusters

Publisher: Elsevier BV

Date: 03-2005

DOI: 10.1016/J.JORGANCHEM.2004.12.018

Mechanism of Pd-Catalyzed Ar–Ar Bond Formation Involving Ligand-Directed C–H Arylation and Diaryliodonium Oxidants: Computational Studies of Orthopalladation at Binuclear Pd(II) Centers, Oxidation To

Publisher: American Chemical Society (ACS)

Date: 09-01-2013

DOI: 10.1021/OM301013W

DFT Mechanistic Investigation into BF3-Catalyzed Alcohol Oxidation by a Hypervalent Iodine(III) Compound

Publisher: American Chemical Society (ACS)

Date: 06-06-2019

DOI: 10.1021/ACSCATAL.9B01599

Molecular Modelling and Design of Radiolabelled Complexes for Melanoma Diagnosis

Publisher: CSIRO Publishing

Date: 2004

DOI: 10.1071/CH03165

Abstract: Molecular modelling has been used to analyze a database of compounds with known binding affinities for the integrin receptors αVβ3 and αIIbβ3. We describe how a variety of novel radiolabelled compounds (specifically 131I labelled) were designed and how the binding affinity of these compounds to the two integrin receptors was predicted. The selectivity for the αVβ3 receptor has also been predicted and a summary of some of the best candidates for positron emission tomography (PET) imaging is provided. This work will have significant implications for the development of diagnostic (and possibly therapeutic) drugs for melanomas.

Synthetic and computational studies of the palladium(iv) system Pd(alkyl)(aryl)(alkynyl)(bidentate)(triflate) exhibiting selectivity in C-C reductive elimination

Publisher: Royal Society of Chemistry (RSC)

Date: 2012

DOI: 10.1039/C2DT31086D

Abstract: Synthetic routes to methyl(aryl)alkynylpalladium(IV) motifs are presented, together with studies of selectivity in carbon-carbon coupling by reductive elimination from Pd(IV) centres. The iodonium reagents IPh(C≡CR)(OTf) (R = SiMe(3), Bu(t), OTf = O(3)SCF(3)) oxidise Pd(II)Me(p-Tol)(L(2)) (1-3) [L(2) = 1,2-bis(dimethylphosphino)ethane (dmpe) (1), 2,2'-bipyridine (bpy) (2), 1,10-phenanthroline (phen) (3)] in acetone-d(6) or toluene-d(9) at -80 °C to form complexes Pd(IV)(OTf)Me(p-Tol)(C≡CR)(L(2)) [R = SiMe(3), L(2) = dmpe (4), bpy (5), phen (6) R = Bu(t), L(2) = dmpe (7), bpy (8), phen (9)] which reductively eliminate predominantly (>90%) p-Tol-C≡CR above ~-50 °C. NMR spectra show that isomeric mixtures are present for the Pd(IV) complexes: three for dmpe complexes (4, 7), and two for bpy and phen complexes (5, 6, 8, 9), with reversible reduction in the number of isomers to two occurring between -80 °C and -60 °C observed for the dmpe complex 4 in toluene-d(8). Kinetic data for reductive elimination from Pd(IV)(OTf)Me(p-Tol)(C≡CSiMe(3))(dmpe) (4) yield similar activation parameters in acetone-d(6) (66 ± 2 kJ mol(-1), ΔH(‡) 64 ± 2 kJ mol(-1), ΔS(‡)-67 ± 2 J K(-1) mol(-1)) and toluene-d(8) (E(a) 68 ± 3 kJ mol(-1), ΔH(‡) 66 ± 3 kJ mol(-1), ΔS(‡)-74 ± 3 J K(-1) mol(-1)). The reaction rate in acetone-d(6) is unaffected by addition of sodium triflate, indicative of reductive elimination without prior dissociation of triflate. DFT computational studies at the B97-D level show that the energy difference between the three isomers of 4 is small (12.6 kJ mol(-1)), and is similar to the energy difference encompassing the six potential transition state structures from these isomers leading to three feasible C-C coupling products (13.0 kJ mol(-1)). The calculations are supportive of reductive elimination occurring directly from two of the three NMR observed isomers of 4, involving lower activation energies to form p-TolC≡CSiMe(3) and earlier transition states than for other products, and involving coupling of carbon atoms with higher s character of σ-bonds (sp(2) for p-Tol, sp for C≡C-SiMe(3)) to form the product with the strongest C-C bond energy of the potential coupling products. Reductive elimination occurs predominantly from the isomer with Me(3)SiC≡C trans to OTf. Crystal structure analyses are presented for Pd(II)Me(p-Tol)(dmpe) (1), Pd(II)Me(p-Tol)(bpy) (2), and the acetonyl complex Pd(II)Me(CH(2)COMe)(bpy) (11).

Phosphine and solvent effects on oxidative addition of CH3Br to Pd(PR3) and Pd(PR3)2 complexes

Publisher: Royal Society of Chemistry (RSC)

Date: 2011

DOI: 10.1039/C1DT10983A

Abstract: The reaction between bromomethane CH(3)Br and Pd(0) phosphine complexes Pd(PR(3)) and Pd(PR(3))(2) resulting in the corresponding Pd(II) species Pd(PR(3))(CH(3))Br and Pd(PR(3))(2)(CH(3))Br was studied computationally with DFT methods. The oxidative addition can take place through two different mechanisms: concerted or S(N)2 transition state. The effect of a number of variables on the height of the barrier associated to each of these two mechanisms is systematically analyzed. The variables considered include the number of ligands on the metal (mono- or bis-phosphine), the nature of the phosphine (PF(3), PH(3), PMe(3) or PPh(3)), and the nature of the solvent (gas phase, tetrahydrofuran or dimethylformamide). A number of trends can be identified, resulting in a complex picture where the nature of the phosphine and the solvent can be tuned to favor one of the two possible mechanisms, with the corresponding stereochemical implications that can be extrapolated to the behaviour of more sophisticated substrates.

The influence of peripheral ligand bulk on nitrogen activation by three‐coordinate molybdenum complexes—A theoretical study using the ONIOM method

Publisher: Wiley

Date: 05-03-2009

DOI: 10.1002/JCC.21199

Abstract: Electronic structure methods have been combined with the ONIOM approach to carry out a comprehensive study of the effect of ligand bulk on the activation of dinitrogen with three-coordinate molybdenum complexes. Calculations were performed with both density functional and CCSD(T) methods. Our results show that not only is there expected destabilization of the intermediate on the pathway due to direct steric interactions of the bulky groups, but also there is significant electronic destabilization as the size of the ligand increases. This latter destabilization is due to the inability of the molecule to accommodate a rotated amide group bound to the molybdenum once the amide reaches a certain size. This destabilization also leads to a clear preference for the triplet intermediate (rather than the singlet intermediate) for bulky substituents which is in agreement with experiment. Overall, the calculated reaction profile for the bulky substituents shows a good correlation with the available experimental data.

An Innovative Approach Characterising the Interactions Leading to Pitch Deposition

Publisher: Informa UK Limited

Date: 2004

DOI: 10.1081/WCT-200026562

Theoretical investigation into the mechanism of reductive elimination from bimetallic palladium complexes

Publisher: American Chemical Society (ACS)

Date: 14-06-2011

DOI: 10.1021/IC102323S

Abstract: Reductive elimination of C-Cl and C-C bonds from binuclear organopalladium complexes containing Pd-Pd bonds with overall formal oxidation state +III are explored by density functional theory for dichloromethane and acetonitrile solvent environments. An X-ray crystallographically authenticated neutral complex, [(L-C,N)ClPd(μ-O(2)CMe)](2) (L = benzo[h]quinolinyl) (I), is examined for C-Cl coupling, and the proposed cation, [(L-C,N)PhPd(1)(μ-O(2)CMe)(2)Pd(2)(L-C,N)](+) (II), examined for C-C coupling together with (L-C,N)PhPd(1)(μ-O(2)CMe)(2)Pd(2)Cl(L-C,N) (III) as a neutral analogue of II. In both polar and nonpolar solvents, reaction from III via chloride dissociation from Pd(2) to form II is predicted to be favored. Cation II undergoes Ph-C coupling at Pd(1) with concomitant Pd(1)-Pd(2) lengthening and shortening of the Pd(1)-O bond trans to the carbon atom of L natural bond orbital analysis indicates that reductive coupling from II involves depopulation of the d(x(2)-y(2)) orbital of Pd(1) and population of the d(z(2)) orbitals of Pd(1) and Pd(2) as the Pd-Pd bond lengthens. Calculations for the symmetrical dichloro complex I indicate that a similar dissociative pathway for C-Cl coupling is competitive with a direct (nondissociative) pathway in acetonitrile, but the direct pathway is favored in dichloromethane. In contrast to the dissociative mechanism, direct coupling for I involves population of the d(x(2)-y(2)) orbital of Pd(1) with Pd(1)-O(1) lengthening, significantly less population occurs for the d(z(2)) orbital of Pd(1) than for the dissociative pathway, and d(z(2)) at Pd(2) is only marginally populated resulting in an intermediate that is formally a Pd(1)(I)-Pd(2)(III) species, (L-Cl-N,Cl)Pd(1)(μ-O(2)CMe)Pd(2)Cl(O(2)CMe)(L-C,N) that releases chloride from Pd(2) with loss of Pd(I)-Pd(III) bonding to form a Pd(II) species. A similar process is formulated for the less competitive direct pathway for C-C coupling from III, in this case involving decreased population of the d(z(2)) orbital of Pd(2) and strengthening of the Pd(I)-Pd(III) interaction in the analogous intermediate with η(2)-coordination at Pd(1) by L-Ph-N, C(1)-C(2).

Computational organic chemistry

Publisher: Royal Society of Chemistry (RSC)

Date: 2006

DOI: 10.1039/B518099F

Dual Gold‐Catalyzed Cycloaromatization of Unconjugated (E)‐Enediynes

Publisher: Wiley

Date: 16-01-2019

DOI: 10.1002/ANGE.201810794

Trust and Consumer Preferences for Pig Production Attributes in Canada

Publisher: Wiley

Date: 09-05-2017

DOI: 10.1111/CJAG.12138

Oxidation of Lignin model compounds containing an alpha-carbonyl group and a ring-conjugated double-bond by hydrogen peroxide-UV photolysis

Publisher: Walter de Gruyter GmbH

Date: 1996

DOI: 10.1515/HFSG.1996.50.3.226

Dinitrogen Activation by Fryzuk’s [Nb(P₂N₂)] Complex and Comparison with the Laplaza–Cummins [Mo{N(R)Ar}₃] and Schrock [Mo(N₃N)] Systems

Publisher: Wiley

Date: 20-10-2009

DOI: 10.1002/CHEM.200900539

Abstract: The reaction profile of N(2) with Fryzuk's [Nb(P(2)N(2))] (P(2)N(2)=PhP(CH(2)SiMe(2)NSiMe(2)CH(2))(2)PPh) complex is explored by density functional calculations on the model [Nb(PH(3))(2)(NH(2))(2)] system. The effects of ligand constraints, coordination number, metal and ligand donor atom on the reaction energetics are examined and compared to the analogous reactions of N(2) with the three-coordinate Laplaza-Cummins [Mo{N(R)Ar}(3)] and four-coordinate Schrock [Mo(N(3)N)] (N(3)N=[(RNCH(2)CH(2))(3)N](3-)) systems. When the model system is constrained to reflect the geometry of the P(2)N(2) macrocycle, the N--N bond cleavage step, via a N(2)-bridged dimer intermediate, is calculated to be endothermic by 345 kJ mol(-1). In comparison, formation of the single-N-bridged species is calculated to be exothermic by 119 kJ mol(-1), and consequently is the thermodynamically favoured product, in agreement with experiment. The orientation of the amide and phosphine ligands has a significant effect on the overall reaction enthalpy and also the N--N bond cleavage step. When the ligand constraints are relaxed, the overall reaction enthalpy increases by 240 kJ mol(-1), but the N(2) cleavage step remains endothermic by 35 kJ mol(-1). Changing the phosphine ligands to amine donors has a dramatic effect, increasing the overall reaction exothermicity by 190 kJ mol(-1) and that of the N--N bond cleavage step by 85 kJ mol(-1), making it a favourable process. Replacing Nb(II) with Mo(III) has the opposite effect, resulting in a reduction in the overall reaction exothermicity by over 160 kJ mol(-1). The reaction profile for the model [Nb(P(2)N(2))] system is compared to those calculated for the model Laplaza and Cummins [Mo{N(R)Ar}(3)] and Schrock [Mo(N(3)N)] systems. For both [Mo(N(3)N)] and [Nb(P(2)N(2))], the intermediate dimer is calculated to lie lower in energy than the products, although the final N-N cleavage step is much less endothermic for [Mo(N(3)N)]. In contrast, every step of the reaction is favourable and the overall exothermicity is greatest for [Mo{N(R)Ar}(3)], and therefore this system is predicted to be most suitable for dinitrogen cleavage.

Structural and electronic characterisation of the organometallic distonic ion (C6H6)Fe+(p-C6H4)

Publisher: Elsevier BV

Date: 07-2000

DOI: 10.1016/S1387-3806(00)00227-X

Competing reaction mechanisms for the carbonylation of neutral palladium(II) complexes containing bidentate ligands: a theoretical study

Publisher: American Chemical Society (ACS)

Date: 07-1997

DOI: 10.1021/OM970063Z

Mechanistic investigation of the oxidation of hydrazides: Implications for the activation of the TB drug isoniazid

Publisher: Royal Society of Chemistry (RSC)

Date: 2013

DOI: 10.1039/C2OB26419F

Abstract: Aryl hydrazides are oxidised to acyl radicals through a mechanism involving diimide intermediates that are prone to nucleophilic acyl substitution. This oxidation occurs regardless of the oxidant involved, however there is no evidence that the acyl radical formed undergoes further oxidation to the corresponding acylium ion, even in the presence of strong oxidants. This study may provide insight into the mechanism of isoniazid resistance in Mycobacterium tuberculosis.

In-depth insight into the electronic and steric effects of phosphine ligands on the mechanism of the R–R reductive elimination from (PR3)2PdR2

Publisher: Elsevier BV

Date: 06-2009

DOI: 10.1016/J.JORGANCHEM.2009.02.011

The structure of a methylpalladium(II) complex of pyridine-2-carboxylato(N-O) and triphenylphosphine (PPh3), [Pd(CH3)(N O)(PPh3)]

Publisher: CSIRO Publishing

Date: 2000

DOI: 10.1071/CH00064

Abstract: The compound [Pd(CH3)(PPh3)(N–O)] (N–O represents pyridine-2-carboxylato (pyca)) has been synthesized and the structure determined. The compound crystallized in the monoclinic space group P21/c, a 8.4844(9), b 12.845(2), c 19.690(3) Å, b 92.09(1)˚, V 2144.4(5) Å 3 , Z 4, and was refined to an R value of 0.022 on 3551 F. The structure had a distorted square-planar geometry in which the donor nitrogen and phosphine ligands are trans.

Reduction of a chelating bis(NHC) palladium(II) complex to [{μbis( NHC)}2Pd2H]+: A terminal hydride in a binuclear palladium(I) species formed under catalytically relevant conditions

Publisher: Wiley

Date: 19-08-2010

DOI: 10.1002/ANIE.201003177

Theoretical studies of the oxidative addition of azolium salts to a model Wilkinson's catalyst

Publisher: Royal Society of Chemistry (RSC)

Date: 2004

DOI: 10.1039/B407088G

Abstract: The oxidative addition of 1,3-dimethylimidazolium to a model Wilkinson's catalyst (RhCl(PH(3))(3)) has been studied with density functional calculations (B3LYP). According to our free energy calculations, the octahedral rhodium carbene hydride product forms from initial predissociation of a phosphine molecule to subsequently form a 5 ligand intermediate however, results indicate that a six ligand, associative route with a concerted three-centred transition structure may also be competitive. Exchange of the phosphine molecule on the metal centre with trimethylphosphine had a significant effect in lowering the barrier to oxidative addition and decreasing the endothermicity of the reaction. Solvation was found to have a moderate effect on the overall reaction. Bulk solvent calculations reflected a relative stabilisation of reactants for both pathways, resulting in an endothermic overall reaction. A study of alternative azolium salts revealed the saturated 1,3-dimethyl-4,5-dihydroimidazolium resulted in little change to the reaction geometries or energies, while the use of 3-methylthiazolium salt significantly reduced the barrier to addition and increased the exothermicity of the reaction considerably.

Cleavage of Carbon Dioxide by an Iridium-Supported Fischer Carbene. A DFT Investigation

Publisher: American Chemical Society (ACS)

Date: 04-2009

DOI: 10.1021/JA809320X

Abstract: The reaction of CO(2), OCS, and PhNCO with an iridium-supported Fischer alkoxycarbene has been investigated with density functional theory. We have confirmed the mechanism for the important CO(2) reaction and successfully rationalized the selective cleavage of the CS and CN bonds in OCS and PhNCO. Armed with this information we have used our model to predict that the same iridium system will preferentially cleave the CS bond in methyl thiocyanate (MeNCS) rather than the CN bond. The formation of the iridium-supported carbene itself has also been investigated and a fascinating autocatalytic mechanism has been discovered which nicely fits the observed experimental behavior.

Theoretical Approaches To Estimating Homolytic Bond Dissociation Energies of Organocopper and Organosilver Compounds

Publisher: American Chemical Society (ACS)

Date: 27-08-2012

DOI: 10.1021/JP305718Z

Abstract: Although organocopper and organosilver compounds are known to decompose by homolytic pathways among others, surprisingly little is known about their bond dissociation energies (BDEs). In order to address this deficiency, the performance of the DFT functionals BLYP, B3LYP, BP86, TPSSTPSS, BHandHLYP, M06L, M06, M06-2X, B97D, and PBEPBE, along with the double hybrids, mPW2-PLYP, B2-PLYP, and the ab initio methods, MP2 and CCSD(T), have been benchmarked against the thermochemistry for the M-C homolytic BDEs (D(0)) of Cu-CH(3) and Ag-CH(3), derived from guided ion beam experiments and CBS limit calculations (D(0)(Cu-CH(3)) = 223 kJ·mol(-1) D(0)(Ag-CH(3)) = 169 kJ·mol(-1)). Of the tested methods, in terms of chemical accuracy, error margin, and computational expense, M06 and BLYP were found to perform best for homolytic dissociation of methylcopper and methylsilver, compared with the CBS limit gold standard. Thus the M06 functional was used to evaluate the M-C homolytic bond dissociation energies of Cu-R and Ag-R, R = Et, Pr, iPr, tBu, allyl, CH(2)Ph, and Ph. It was found that D(0)(Ag-R) was always lower (~50 kJ·mol(-1)) than that of D(0)(Cu-R). The trends in BDE when changing the R ligand reflected the H-R bond energy trends for the alkyl ligands, while for R = allyl, CH(2)Ph, and Ph, some differences in bond energy trends arose. These trends in homolytic bond dissociation energy help rationalize the previously reported (Rijs, N. J. O'Hair, R. A. J. Organometallics2010, 29, 2282-2291) fragmentation pathways of the organometallate anions, [CH(3)MR](-).

Density Functional Theory Studies on the Oxidation of 5′-dGMP and 5′-dAMP by a Platinum(IV) Complex

Publisher: American Chemical Society (ACS)

Date: 18-07-2012

DOI: 10.1021/IC300038M

Abstract: Density functional theory has been used to investigate the oxidation of a guanine nucleotide by platinum(IV), a process that can be important in the degradation of DNA. For the first time, we have provided a comprehensive mechanism for all of the steps in this process. A number of intermediates are predicted to occur but with short lifetimes that would make them difficult to observe experimentally. A key step in the mechanism is electron transfer from guanine to platinum(IV), and we show that this is driven by the loss of a chloride ligand from the platinum complex after nucleophilic attack of 5'-phosphate to C8 of guanine. We have investigated several different initial platinum(IV) guanine adducts and shown that the adduct formed from replacement of an axial chlorine ligand in the platinum(IV) complex undergoes oxidation more easily. We have studied adenine versus guanine adducts, and our results show that oxidation of the former is more difficult because of disruption of the aromatic π system that occurs during the process. Finally, our results show that the acidic hydrolysis step to form the final oxidized product occurs readily via an initial protonation of N7 of the guanine.

A Theoretical Study on the Protodeauration Step of the Gold(I)-Catalyzed Organic Reactions

Publisher: American Chemical Society (ACS)

Date: 23-06-2015

DOI: 10.1021/ACS.ORGANOMET.5B00219

NO₂bond cleavage by MoL₃complexes

Publisher: Royal Society of Chemistry (RSC)

Date: 2014

DOI: 10.1039/C3DT52554F

Abstract: The cleavage of one N-O bond in NO2 by two equivalents of Mo(NRAr)3 has been shown to occur to form molybdenum oxide and nitrosyl complexes. The mechanism and electronic rearrangement of this reaction was investigated using density functional theory, using both a model Mo(NH2)3 system and the full [N((t)Bu)(3,5-dimethylphenyl)] experimental ligand. For the model ligand, several possible modes of coordination for the resulting complex were observed, along with isomerisation and bond breaking pathways. The lowest barrier for direct bond cleavage was found to be via the singlet η(2)-N,O complex (7 kJ mol(-1)). Formation of a bimetallic species was also possible, giving an overall decrease in energy and a lower barrier for reaction (3 kJ mol(-1)). Results for the full ligand showed similar trends in energies for both isomerisation between the different isomers, and for the mononuclear bond cleavage. The lowest calculated barrier for cleavage was only 21 kJ mol(-1)via the triplet η(1)-O isomer, with a strong thermodynamic driving force to the final products of the doublet metal oxide and a molecule of NO. Formation of the full ligand dinuclear complex was not accompanied by an equivalent decrease in energy seen with the model ligand. Direct bond cleavage via an η(1)-O complex is thus the likely mechanism for the experimental reaction that occurs at ambient temperature and pressure. Unlike the other known reactions between MoL3 complexes and small molecules, the second equivalent of the metal does not appear to be necessary, but instead irreversibly binds to the released nitric oxide.

Dinitrogen metal complexes with a strongly activated N–N bond: a computational investigation of [(Cy2N)3Nb-(μ-NN)-Nb(NCy2)3] and related [Nb-(μ-NN)-Nb] systems

Publisher: Royal Society of Chemistry (RSC)

Date: 2012

DOI: 10.1039/C2DT31845H

Abstract: The structural and bonding properties of the dinitrogen-bridged diniobium [(Cy(2)N)(3)Nb(μ-NN)Nb(NCy(2))(3)] complex experimentally characterized by Berno and Gambarotta, which exhibits a strongly activated N-N bond of 134 pm, have been explored using density functional methods and compared with those of a series of related [(R(2)N)(3)Nb(μ-NN)Nb(NR(2))(3)] (R = H, Me, (i)Pr, (t)Bu, Cy) model species and other experimentally relevant [Nb(μ-NN)Nb] systems, in order to rationalize the unusually long N-N distance. Geometry optimizations of [(Cy(2)N)(3)Nb(μ-NN)Nb(NCy(2))(3)] and three other known systems indicate that the most favourable N-N distance lies within the range of commonly reported results for end-on bound dinitrogen-diniobium complexes, between 123 and 128 pm. However, structures exhibiting appreciably longer N-N distances, close to 134 pm, are found to be only weakly disfavoured, and may represent the preferred geometry in cases where lengthening of the N-N bond counteracts the effects of highly repulsive steric interactions between terminal fragments. Calculations on model complexes, in which small-sized [R = H, Me] terminal groups are involved, support the finding that N-N bond lengths within the 123-128 pm range are most favoured, whereas calculations on larger [R = (i)Pr, (t)Bu] model species indicate that the presence of excessively repulsive intramolecular interactions can lead to substantial changes in the geometric properties of the [Nb-NN-Nb] core, including significant increase in N-N bond length and activation. The preference for N-N distances ranging between 123 and 128 pm, irrespective of ligand size and identity, can be understood on the basis that the principal bonding mechanisms across the central [Nb-NN-Nb] core are largely unaffected by changes in the chemical composition and properties of terminal fragments. However, the balance between repulsive (steric) and attractive (electrostatic plus orbital) bonding contributions can be altered by the presence of geometrically rigid and oversized peripheral groups and, in these cases, the interplay between repulsive and attractive bonding effects is dominated by the former and can result in abnormally elongated N-N distances. The present calculations thus provide a rationale for the observed structural properties of the [(Cy(2)N)(3)Nb(μ-NN)Nb(NCy(2))(3)] system on the basis of the interplay between electronic and steric factors.

Revisiting the Aufbau reaction with acetylene: Further insights from experiment and theory

Publisher: American Chemical Society (ACS)

Date: 23-02-2011

DOI: 10.1021/OM101114C

Nazarov cyclisations initiated by DDQ-oxidised pentadienyl ether: a mechanistic investigation from the DFT perspective

Publisher: Royal Society of Chemistry (RSC)

Date: 2018

DOI: 10.1039/C8OB02590H

Abstract: The rate determining step for such a Nazarov cyclization is direct hydride transfer from pentadienyl ether to the oxygen of DDQ.

Hydroalkylation of Alkenes with 1,3-Diketones via Gold(III) or Silver(I) Catalysis: Divergent Mechanistic Pathways Revealed by a DFT-Based Investigation

Publisher: American Chemical Society (ACS)

Date: 27-04-2021

DOI: 10.1021/ACSCATAL.0C05260

Dual Gold‐Catalyzed Cycloaromatization of Unconjugated (E)‐Enediynes

Publisher: Wiley

Date: 17-01-2019

DOI: 10.1002/ANIE.201810794

Abstract: A synthesis of unconjugated (E)-enediynes from allenyl amino alcohols is reported and their gold-catalyzed cascade cycloaromatization to a broad range of enantioenriched substituted isoindolinones has been developed. Experimental and computational studies support the reaction proceeding via a dual-gold σ,π-activation mode, involving a key gold-vinylidene- and allenyl-gold-containing intermediate.

Activation and cleavage of the N–N bond in side-on bound [L2M-NN-ML2] (L = NH2, NMe2, NiPr2, C5H5, C5Me4H) dinitrogen complexes of transition metals from groups 4 through 9

Publisher: Royal Society of Chemistry (RSC)

Date: 2010

DOI: 10.1039/B924999K

Abstract: The activation and cleavage of the N-N bond in side-on bound [L₂M-NN-ML₂] (L = NH₂, NMe₂, N(i)Pr₂, C₅H₅, C₅Me₄H) dinitrogen complexes of transition metals in groups 4 through 9 have been investigated using density functional theory. Emphasis has been placed on Ti, Zr, and Hf (group 4) complexes due to their experimental relevance. Calculations on these species have shown that for cases when the structural configuration corresponds to the terminal [ML₂] fragments adopting a perpendicular orientation with respect to the central [N-N] unit, a considerably higher degree of N-N activation is predicted relative to that observed in the experimentally characterized cyclopentadienyl analogues and in related systems involving end-on dinitrogen coordination. An examination of the orbital interactions between the metal-based fragments and the dinitrogen unit shows that both σ and π bonding are important in the side-on binding mode, in contrast to the end-on mode where metal-nitrogen π interactions are dominant. This analysis also reveals that the model amide systems possess the orbital properties identified as necessary for successful N-N hydrogenation. A significant result obtained for the amide complexes containing metals from groups 5 (V, Nb, Ta), 6 (Cr, Mo, W), and 7 (Mn, Tc, Re), is the presence of metal-metal bonding in configurations that are considerably distorted from planarity. As a consequence, these complexes exhibit strongly enhanced stability relative to species where metal-metal bonding is absent. In contrast, the d² metal-based configurations in the group 4 complexes of Ti, Zr, and Hf are unable to provide the six electrons required for complete reductive cleavage of the dinitrogen unit which is necessary to allow the metal centres to approach one another sufficiently for metal-metal bond formation.

A mechanistic study on the oxidation of hydrazides: Application to the tuberculosis drug isoniazid

Publisher: Royal Society of Chemistry (RSC)

Date: 2008

DOI: 10.1039/B719570B

Abstract: Herein we report radical trapping experiments that support the formation of an acyl radical as the active species from the oxidation of isoniazid these data provide insight into the mechanism of hydrazide oxidation.

Hybrid supermolecule-polarizable continuum approach to solvation: application to the mechanism of the Stevens Rearrangement

Publisher: Wiley

Date: 09-1996

DOI: 10.1002/(SICI)1096-987X(199609)17:12<1444::AID-JCC5>3.0.CO;2-K

Oxidative addition of 2-substituted azolium salts to Group-10 metal zero complexes—A DFT study

Publisher: Royal Society of Chemistry (RSC)

Date: 2007

DOI: 10.1039/B709914B

Abstract: Generation of N-heterocyclic carbene (NHC) complexes [(dmpe)M(azol-2-ylidene)R] via the oxidative addition of a series of 2-substituted azolium salts to Group-10 zerovalent metal complexes has been investigated using density functional theory (2-R = H, Me, Ph Azole = imidazole, thiazole, oxazole M = Ni, Pd, Pt). Overall, platinum-based pathways result in the greatest enthalpies of reaction, but due to the reactive nature of Group-10 metals bearing the 1,2-bis(dimethylphosphino)ethane (dmpe) chelate, nickel and palladium species also have little trouble proceeding to stable products in the absence of a significant barrier. Imidazolium salts were found to be the most vulnerable to oxidative addition due to their low stabilisation energies when compared to the oxazolium and thiazolium species. Activation barriers show the general trend of phenyl > methyl > hydrido with regard to the azole 2-substituent, with no observed barrier for all but one of the 2-hydrido cases. Minimal barriers were found to exist in a number of cases for activation of a C(2)-CH3 bond suggesting that synthesis of alkyl-carbene complexes may be possible via this route under certain conditions, and therefore ionic liquids based on these substituted azolium salts may be active participants in catalytic reactions.

An Assessment of Theoretical Protocols for Calculation of the pKa Values of the Prototype Imidazolium Cation

Publisher: CSIRO Publishing

Date: 2004

DOI: 10.1071/CH04159

Abstract: The highly accurate complete basis set method CBS-QB3 has been used in conjunction with the conductor-like polarized continuum (CPCM) method to predict the aqueous pKa values for the three different hydrogen atoms in the imidazolium cation. Excellent agreement was obtained with the available experimental values. The pKa for the deprotonation of imidazole was also calculated and found to be quite different from the experimental estimate. The protocol for the pKa calculation was carefully analyzed and some recommendations made about the choice of levels of theory.

Borane-Catalyzed Stereoselective C–H Insertion, Cyclopropanation, and Ring-Opening Reactions

Publisher: Elsevier BV

Date: 09-2020

DOI: 10.1016/J.CHEMPR.2020.06.035

Synthesis of N-heterocyclic carbene palladium(ii) bis-phosphine complexes and their decomposition in the presence of aryl halides

Publisher: Royal Society of Chemistry (RSC)

Date: 2007

DOI: 10.1039/B706053J

Abstract: Methylpalladium(II) carbene complexes of the type [Pd(NHC)Me(P-P)]BF(4) (NHC = N-heterocyclic carbene, P-P = chelating phosphine) have been synthesised, the complex [Pd(tmiy)Me(dcype)]BF(4) (tmiy = 1,3,4,5-tetramethylimidazol-2-ylidene, dcype = 1,2-bis(dicyclohexylphosphino)ethane) being characterised crystallographically. Complexes bearing the tmiy ligands were shown to decompose in an analogous manner to complexes bearing monodentate phosphine ligands, with the rate of decomposition being nominally linked to the size of the chelate ring. The decomposition of these complexes in the presence of aryl halides-expected to yield Pd(Ar)X(P-P)-was studied and shown instead to yield PdX(2)(P-P) and [Pd(tmiy)X(P-P)]BF(4). Additionally, Pd(Me)X(P-P) and Pd(Ar)X(P-P) were observed in some cases. Intermolecular cross-over reactions between the starting complex and Pd(Ar)X(P-P) were found to be the source of these unexpected products.

The influence of N-substitution on the reductive elimination behaviour of hydrocarbyl–palladium–carbene complexes—a DFT study

Publisher: Royal Society of Chemistry (RSC)

Date: 2006

DOI: 10.1039/B512681A

Abstract: The reductive elimination of 2-hydrocarbyl-imidazolium salts from hydrocarbyl-palladium complexes bearing N-heterocyclic carbene (NHC) ligands represents an important deactivation route for catalysts of this type. We have explored the influence that carbene N-substituents have on both the activation energy and the overall thermodynamics of the reductive elimination reaction using density functional theory (DFT). Given the proximity of the N-substituent to the three-centred transition structure, steric bulk has little influence on the activation barrier and it is electronic factors that dominate the barriers' magnitude. Increased electron donation from the departing NHC ligand acts to stabilise the associated complex against reductive elimination, with stability following the trend: Cl < H < Ph < Me < Cy < iPr < neopentyl < tBu. The intimate involvement of the carbene p pi-orbital in determining the barrier to reductive elimination means N-substituents that are capable of removing pi-density (e.g. phenyl) act to promote a more facile reductive elimination.

Rationale for the reactivity differences between main group and d0 transition metal complexes toward olefin polymerisation

Publisher: Royal Society of Chemistry (RSC)

Date: 2019

DOI: 10.1039/C9DT01017C

Abstract: A ring strain in a four-membered ring transition structure plays an important role in controlling the activation barrier to an olefin insertion into a M–R bond.

Oxazoles revisited: On the nature of binding of benzoxazole and 2-methylbenzoxazole with the zinc and palladium halides

Publisher: Royal Society of Chemistry (RSC)

Date: 2011

DOI: 10.1039/C0DT01266A

Abstract: A synthetic and structural (X-ray) investigation into the bonding modes of benzoxazole (box) and 2-methylbenzoxazole (Mebox) ligands with halide precursors of Zn and Pd has been undertaken to clarify earlier discrepancies concerning the nature of the bonding mode(s) of the two azoles. In four structurally characterised ex les, all contain the title ligands in a κ(1)N bonding motif. Calculations at the density functional level (DFT) of theory (B3LYP) confirm the ground state stability of this class of coordination for several hypothetical Pd and Zn (gas phase) compounds. The attempt to obtain suitable crystalline material of PdCl(2)(box)(2) (i.e., 5) leads to substantial complex degradation. One minor product of this process has been identified (X-ray) as the diarylformamidinato complex C(26)H(22)N(4)O(4)Pd, presumably formed via a complex combination of the decomposition products of both free box and 5.

DFT-Based Comparison between Mechanistic Aspects of Amine and Alcohol Oxidation Mediated by IBX

Publisher: American Chemical Society (ACS)

Date: 26-12-2020

DOI: 10.1021/ACS.JOC.9B02583

Abstract: Density functional theory was utilized to investigate plausible mechanisms for amine and alcohol oxidation by an iodine(V) hypervalent reagent (IBX). In this contribution, we found that amine and alcohol oxidation both proceed by similar mechanisms. The reactions initiate from ligand exchange to give four coordinate intermediates followed by a redox process giving an iodine(III) species and oxidized substrates. Interestingly, for both the ligand-exchange and the redox steps a hypervalent twist is required for the reaction to proceed via an energetically more accessible route. The ligand-exchange process was found to be mediated by a proton-shuttling agent such as water, a second IBX, or a second substrate. While the ligand-exchange step for both amine and alcohol occurs with almost identical activation energy (particularly when water is considered as the shuttling agent), the redox step for the amine takes place with much lower activation energy than that for the alcohol. Finally, we ascertained that five coordinate amide iodine(V) complexes are unreactive toward redox reactions due to the fact that in such cases two electrons from the coordinated amide are required to occupy a 3c-4e σ* orbital which is too high in energy to be reachable.

Competing rearrangements of ammonium ylides: a quantum theoretical study

Publisher: American Chemical Society (ACS)

Date: 1996

DOI: 10.1021/JO952227W

Abstract: The competition between the Stevens [1,2] and Sommelet-Hauser [2,3] rearrangements for a prototype ylide, N-methyl-3-propenylammonium methylide, has been investigated using ab initio and semiempirical molecular orbital methods. The activation energies for the two processes are remarkably close, separated by only 2 kJ mol(-)(1) at ROMP/6-311+G(d,p). Increasing the size of the basis set leads to a relative stabilization of the Sommelet-Hauser transition geometry, while higher levels of electron correlation (such as CCSD(T)) favor the Stevens rearrangement. Incorporation of solvent effects via the SCRF polarizable continuum model leads to a lowering of the energy barrier of the concerted [2,3] rearrangement, but has little effect on the dissociative [1,2] pathway. The activation energies of both pathways have been calculated for ylides bearing substituents on the ammonium nitrogen and the double bond. Substituents at nitrogen lead to an ylide which is sterically unstable and hence a preference for the dissociative [1,2] rearrangement. Electron-withdrawing substituents on the double bond show a preference for the [2,3] rearrangement, while mildly electron-donating alkyl substituents have very little effect on activation energies.

Tris(pentafluorophenyl)borane‐Catalyzed Carbenium Ion Generation and Autocatalytic Pyrazole Synthesis—A Computational and Experimental Study

Publisher: Wiley

Date: 12-10-2021

DOI: 10.1002/ANIE.202109744

Abstract: In recent years, metal‐free organic synthesis using triarylboranes as catalysts has become a prevalent research area. Herein we report a comprehensive computational and experimental study for the highly selective synthesis of N‐substituted pyrazoles through the generation of carbenium species from the reaction between aryl esters and vinyl diazoacetates in the presence of catalytic tris(pentafluorophenyl)borane [B(C 6 F 5 ) 3 ]. DFT studies were undertaken to illuminate the reaction mechanism revealing that the in situ generation of a carbenium species acts as an autocatalyst to prompt the regiospecific formation of N‐substituted pyrazoles in good to excellent yields (up to 81 %).

Dimethylcuprate Undergoes a Dyotropic Rearrangement

Publisher: Wiley

Date: 19-02-2010

DOI: 10.1002/CHEM.200903510

Solution, structural and catalytic studies of neutral MCl2 (M = Pd, Pt) complexes of the N/E mixed-donor ligands 2-(RECH2)C5H4N (RE = MeS, PhS, MeSe)

Publisher: Wiley

Date: 03-2005

DOI: 10.1002/EJIC.200400514

Cationic methylpalladium(II) complexes containing bidentate N-O ligands as catalysts for the copolymerisation of CO and ethylene. Identification and isolation of intermediates from the stepwise insertion reactions, and subsequent detailed mechanistic interpretation

Publisher: Royal Society of Chemistry (RSC)

Date: 1998

DOI: 10.1039/A707199J

Discovery of Periodinane Oxy-Assisted (POA) Oxidation Mechanism in the IBX-Controlled Oxidative Dearomatization of Pyrroles Mediated by Acetic Acid

Publisher: American Chemical Society (ACS)

Date: 26-09-2022

DOI: 10.1021/ACS.JOC.2C01923

Abstract: The 2-iodoxybenzoic acid (IBX)-controlled oxidative dearomatization of pyrroles occurs very slowly (or not all) in many organic solvents, including DMSO in which IBX is soluble. Interestingly, although IBX is only partially soluble in acetic acid, this solvent mediates the pyrrole oxidative dearomatization. With the aid of density functional theory (DFT) calculations, we have discovered a new mode of reactivity, termed the periodinane oxy-assisted (POA) oxidation mechanism, which explains this observation.

Structural studies of group 1 metal 4-azapentalenyl complexes

Publisher: Royal Society of Chemistry (RSC)

Date: 2005

DOI: 10.1039/B500198F

Abstract: The first structurally authenticated 4-azapentalenyl complexes are reported, along with DFT studies, that reveal tendencies for their cyclopentadienyl isostructural nature and an ability to exhibit binding modes of varying hapticity.

Olefin strain energies and platinum complexes of highly pyramidalised alkenes

Publisher: Elsevier BV

Date: 10-2001

DOI: 10.1016/S0022-328X(01)01045-2

How a Bismuth(III) Catalyst Achieves Greatest Activation of Organic Lewis Bases in a Catalytic Reaction: Insights from DFT Calculations

Publisher: Wiley

Date: 25-11-2021

DOI: 10.1002/CCTC.202001688

Reaction of H₂ with a Binuclear Zirconium Dinitrogen Complex − Evaluation of Theoretical Models and Hybrid Approaches

Publisher: American Chemical Society (ACS)

Date: 04-07-2006

DOI: 10.1021/CT050320E

Abstract: Molecular orbital and hybrid ONIOM (both IMOMO and IMOMM) calculations have been carried out on the important reaction of H2 with a binuclear zirconium dinitrogen complex to test the efficacy of several structural models of the ancillary ligand. The complete experimental ligand, PhP(CH2SiMe2NSiMe2CH2)2PPh, in the zirconium complex has been treated at the IMOMM level, while two smaller approximations of the ligand, HP(CH2SiH2NSiH2CH2)2PH and (PH3)2(NH2)2, have received the full molecular orbital treatment. The mechanism of dihydrogen addition has been compared with our earlier study (Basch, Musaev, and Morokuma J. Am. Chem. Soc. 1999, 121, 5754-5761). We find that the substituent effects do cause some small changes in both the structures of the complexes studied and the activation energies of the transition structures. However for the most part the potential energy profiles are very similar to our earlier study and lend support to our use of simple theoretical models to represent moderately large experimental structures.

A Molecular Orbital Rationalization of Ligand Effects in N₂Activation

Publisher: Wiley

Date: 07-07-2008

DOI: 10.1002/CHEM.200800235

Abstract: Molecular orbital theory has been used to study a series of [(micro-N2){ML3}2] complexes as models for dinitrogen activation, with M=Mo, Ta, W, Re and L=NH2, PH2, AsH2, SbH2 and N(BH2)2. The main aims of this study have been to provide a thorough electronic analysis of the complexes and to extend previous work involving molecular orbital analyses. Molecular orbital diagrams have been used to rationalize why for L=NH2 ligand rotation is important for the singlet state but not the triplet, to confirm the effect of ligand pi donation, and to rationalize the importance of the metal d-electron configuration. The outcomes of this study will assist with a more in-depth understanding of the electronic basis for N2 activation and allow clearer predictions to be made about the structure and multiplicity of systems involved in transition-metal catalysis.

Understanding the mechanism of CuI-catalyzed N–H carboxylation of heterocyclic rings with CO2 from a theoretical point of view

Publisher: Elsevier BV

Date: 12-2013

DOI: 10.1016/J.JORGANCHEM.2013.04.060

The platinum-ethylene binding energy in Pt(PL3)2(C2H4)

Publisher: Elsevier BV

Date: 07-2000

DOI: 10.1016/S0166-1280(00)00414-0

Investigating CN^–cleavage by three-coordinate M[N(R)Ar]₃complexes

Publisher: Royal Society of Chemistry (RSC)

Date: 2008

DOI: 10.1039/B713757E

Abstract: Three-coordinate Mo[N((t)Bu)Ar]3 binds cyanide to form the intermediate [Ar((t)Bu)N]3Mo-CN-Mo[N((t)Bu)Ar]3 but, unlike its N2 analogue which spontaneously cleaves dinitrogen, the C-N bond remains intact. DFT calculations on the model [NH2]3Mo/CN- system show that while the overall reaction is significantly exothermic, the final cleavage step is endothermic by at least 90 kJ mol(-1), accounting for why C-N bond cleavage is not observed experimentally. The situation is improved for the [H2N]3W/CN- system where the intermediate and products are closer in energy but not enough for CN- cleavage to be facile at room temperature. Additional calculations were undertaken on the mixed-metal [H2N]3Re+/CN- /W[NH2]3 and [H2N]3Re+/CN-/Ta[NH2]3 systems in which the metals ions were chosen to maximise the stability of the products on the basis of an earlier bond energy study. Although the reaction energetics for the [H2N]3Re+/CN /W[NH2]3 system are more favourable than those for the [H2N]3W/CN- system, the final C-N cleavage step is still endothermic by 32 kJ mol(-1) when symmetry constraints are relaxed. The resistance of these systems to C-N cleavage was examined by a bond decomposition analysis of [H2N]M-L1[triple bond]L2-M[NH2]3 intermediates for L1[triple bond]L2 = N2, CO and CN which showed that backbonding from the metal into the L1[triple bond]L2 pi* orbitals is significantly less for CN than for N2 or CO due to the negative charge on CN- which results in a large energy gap between the metal d(pi), and the pi* orbitals of CN-. This, combined with the very strong M-CN- interaction which stabilises the CN intermediate, makes C-N bond cleavage in these systems unfavourable even though the C[triple bond]N triple bond is not as strong as the bond in N2 or CO.

Competing mechanisms in the carbonylation of neutral palladium(II) complexes containing bidentate ligands: theoretical insights

Publisher: Royal Society of Chemistry (RSC)

Date: 1996

DOI: 10.1039/CC9960000781

Solution, structural and catalytic studies of neutral MCl2 (M = Pd, Pt) complexes of the N/E mixed-donor ligands 2-(RECH2)C5H4N (RE = MeS, PhS, MeSe)

Publisher: Wiley

Date: 03-2005

DOI: 10.1002/EJIC.200400514

DFT Study on the Mechanism of the Activation and Cleavage of CO₂ by (NHC)CuEPh₃ (E = Si, Ge, Sn)

Publisher: American Chemical Society (ACS)

Date: 24-02-2011

DOI: 10.1021/OM100730H

Reactivity of CO2 towards Mo[N(R)Ph]3

Publisher: Royal Society of Chemistry (RSC)

Date: 2009

DOI: 10.1039/B909982D

Abstract: The Laplaza/Cummins L(3)Mo (L = N(R)Ar) system is a very important complex for activating small molecules such as N(2). Previous experimental work has shown that CS(2) binds to the L(3)Mo system and forms an Mo-CS-Mo intermediate, while the environmentally important CO(2) molecule is unreactive. The aim of this paper is to explain why there is this contrast in reactivity. We have used density functional methods to show that at first glance the reaction of 3L(3)Mo + CO(2) should proceed smoothly to give L(3)Mo-O + L(3)Mo-CO-MoL(3). However initial coordination of the CO(2) molecule to L(3)Mo does not take place because of the bending of CO(2), the energy required to cross from the doublet to the quartet state, and the lower metal-CO(2) binding energy compared to metal-CS(2). The subsequent formation of the L(3)Mo-CO-MoL(3) intermediate is similarly unfeasible due to steric and entropic effects. We have provided a molecular orbital rationalization for these effects and have also shown that it is important to take account of steric factors in order to get an accurate understanding of the energetic picture.

Ligand design for alpha(1) adrenoceptor subtype selective antagonists

Publisher: Elsevier BV

Date: 2000

DOI: 10.1016/S0968-0896(99)00263-1

Abstract: Alpha1 adrenoceptors have three subtypes and drugs interacting selectively with these subtypes could be useful in the treatment of a variety of diseases. In order to gain an insight into the structural principles governing subtype selectivity, ligand based drug design (pharmacophore development) methods have been used to design a novel 1,2,3-thiadiazole ring D analogue of the aporphine system. Synthesis and testing of this compound as a ligand on cloned and expressed human alpha1 adrenoceptors is described. Low binding affinity was found, possibly due to an unfavourable electrostatic potential distribution. Pharmacophore models for antagonists at the three adrenoceptor sites (alpha1A, alpha1B, alpha1D) were generated from a number of different training sets and their value for the design of new selective antagonists discussed. The first preliminary antagonist pharmacophore model for the alpha1D adrenoceptor subtype is also reported.

The Mechanism of the Stetter Reaction – A DFT Study

Publisher: Wiley

Date: 11-2008

DOI: 10.1002/EJOC.200800506

Activation and cleavage of the N–O bond in dinuclear mixed-metal nitrosyl systems and comparative analysis of carbon monoxide, dinitrogen, and nitric oxideactivation

Publisher: Royal Society of Chemistry (RSC)

Date: 2009

DOI: 10.1039/B812568F

Abstract: The activation and scission of the N-O bond in nitric oxide using dinuclear mixed-metal species, comprising transition elements with d(3) and d(2) configurations and trisamide ligand systems, have been investigated by means of density functional calculations. The [Cr(iii)-V(iii)] system is analyzed in detail and, for comparative purposes, the [Mo(iii)-Nb(iii)], [W(iii)-Ta(iii)], and (mixed-row) [Mo(iii)-V(iii)] systems are also considered. The overall reaction and in idual intermediate steps are favourable for all systems, including the case where first row (Cr and V) metals are exclusively involved, a result that has not been observed for the related dinitrogen and carbon monoxide systems. In contrast to the cleavage of dinitrogen by three-coordinate Mo amide complexes where the dinuclear intermediate possesses a linear [Mo-NN-Mo] core, the [M-NO-M'] core must undergo significant bending in order to stabilize the dinuclear species sufficiently for the reaction to proceed beyond the formation of the nitrosyl encounter complex. A comparative bonding analysis of nitric oxide, dinitrogen and carbon monoxide activation is also presented. The overall results indicate that the pi interactions are the dominant factor in the bonding across the [M-L(1)L(2)-M'] (L(1)L(2) = N-O, N-N, C-O) moiety and, consequently, the activation of the L(1)-L(2) bond. These trends arise from the fact that the energy gaps between the pi orbitals on the metal and small molecule fragments are much more favourable than for the corresponding sigma orbitals. The pi energy gaps decrease in the order [NO < N(2) < CO] and consequently, for each in idual pi orbital interaction, the back donation between the metal and small molecule increases in the order [CO < N(2) < NO]. These results are in accord with previous findings suggesting that optimization of the pi interactions plays a central role in increasing the ability of these transition metal systems to activate and cleave small molecule bonds.

10  Computational organic chemistry

Publisher: Royal Society of Chemistry (RSC)

Date: 2005

DOI: 10.1039/B500216H

Scission of Carbon Monoxide Using TaR₃, R=(N(tBu)Ph) or OSi(tBu)₃: A DFT Investigation

Publisher: Wiley

Date: 10-06-2010

DOI: 10.1002/CHEM.200903348

Abstract: The experimentally known reduction of carbon monoxide using a 3-coordinate [Ta(silox)(3)] (silox=OSi(tBu)(3)) complex initially forms a ketenylidene [(silox)(3)Ta-CCO], followed by a dicarbide [(silox)(3)Ta-CC-Ta(silox)(3)] structure. The mechanism for this intricate reaction has finally been revealed by using density functional theory, and importantly a likely structure for the previously unknown intermediate [(silox)(3)Ta-CO](2) has been identified. The analysis of the reaction pathway and the numerous intermediates has also uncovered an interesting pattern that results in CO cleavage, that being scission from a structure of the general form [(silox)(3)Ta-C(n)O] in which n is even. When n is odd, cleavage cannot occur. The mechanism has been extended to consider the effect of altering both the metal species and the ligand environment. Specifically, we predict that introducing electron-rich metals to the right of Ta in the periodic table to create mixed-metal dinuclear intermediates shows great promise, as does the ligand environment of the Cummins-style 3-coordinate amide structure. This latter environment has the added complexity of improved electron donation from amide rotation that can significantly increase the reaction exothermicity.

Lanthanide(II) and -(III) porphyrinogens - Rational synthesis and derivatisation of mononuclear, alkali-metal-free lanthanide(II) and -(III) meso-octaalkylporphyrinogen complexes

Publisher: Wiley

Date: 05-2004

DOI: 10.1002/EJIC.200300965

Theoretical Investigation into the Mechanism of 3′-dGMP Oxidation by [Pt^IVCl₄(dach)]

Publisher: American Chemical Society (ACS)

Date: 27-12-2012

DOI: 10.1021/IC3018425

Abstract: The mechanism for the oxidation of 3'-dGMP by [PtCl(4)(dach)] (dach = diaminocyclohexane) in the presence of [PtCl(2)(dach)] has been investigated using density functional theory. We find that the initial complexation, i.e., the formation of [PtCl(3)(dach)(3'-dGMP)], is greatly assisted by the reaction of the encounter pair [PtCl(2)(dach)···3'-dGMP] with [PtCl(4)(dach)], leading to migration of an axial chlorine ligand from platinum(IV) to platinum(II). A dinuclear platinum(II) latinum(IV) intermediate could not be found, but the reaction is predicted to pass through a platinum(III) latinum(III) transition structure. A cyclization process, i.e., C8-O bond formation, from [PtCl(3)(dach)(3'-dGMP)] occurs through an intriguing phosphate-water-assisted deprotonation reaction, analogous to the opposite of a proton shuttle mechanism. Followed by this, the guanine moiety is oxidized via dissociation of the Pt(IV)-Cl(ax) bond, and the cyclic ether product is finally formed after deprotonation. We have provided rationalizations, including molecular orbital explanations, for the key steps in the process. Our results help to explain the effect of [PtCl(4)(dach)] on the complexation step and the effect of a strong hydroxide base on the cyclization reaction. The overall reaction cycle is intricate and involves autocatalysis by a platinum(II) species.

Titelbild: Dual Gold‐Catalyzed Cycloaromatization of Unconjugated (E)‐Enediynes (Angew. Chem. 7/2019)

Publisher: Wiley

Date: 21-12-2019

DOI: 10.1002/ANGE.201814227

ESR study of lignin model compounds irradiated by UV (254nm photons) in the presence of hydrogen peroxide

Publisher: Walter de Gruyter GmbH

Date: 1996

DOI: 10.1515/HFSG.1996.50.3.233

Oxidation of Electron-Deficient Phenols Mediated by Hypervalent Iodine(V) Reagents: Fundamental Mechanistic Features Revealed by a Density Functional Theory-Based Investigation

Publisher: American Chemical Society (ACS)

Date: 19-08-2021

DOI: 10.1021/ACS.JOC.1C01545

Theoretical study of the mechanism for the sequential N–O and N–N bond cleavage within N₂O adducts of N-heterocyclic carbenes by a vanadium(iii) complex

Publisher: Royal Society of Chemistry (RSC)

Date: 2016

DOI: 10.1039/C5DT03600C

Abstract: The addition of N -heterocyclic carbene (NHC) increases the activity of N 2 O towards cleavage of both the N–O and N–N bonds.

A Mechanistic Investigation of the Gold(III)-Catalyzed Hydrofurylation of C–C Multiple Bonds

Publisher: American Chemical Society (ACS)

Date: 28-10-2016

DOI: 10.1021/JACS.6B05742

Abstract: The gold-catalyzed direct functionalization of aromatic C-H bonds has attracted interest for constructing organic compounds which have application in pharmaceuticals, agrochemicals, and other important fields. In the literature, two major mechanisms have been proposed for these catalytic reactions: inner-sphere syn-addition and outer-sphere anti-addition (Friedel-Crafts-type mechanism). In this article, the AuCl

Ligand substitution: An assessment of the reliability of ab initio calculations

Publisher: American Chemical Society (ACS)

Date: 1996

DOI: 10.1021/JP960831K

Increased Stability of NO and NS Heterocyclic Carbenes?

Publisher: CSIRO Publishing

Date: 2004

DOI: 10.1071/CH03248

Abstract: Density functional theory has been used to investigate the effects of alkylation and oxidation on the stability of NO and NS heterocyclic carbenes. While O- and S-alkylation leads to a dramatic increase in stability with respect to dimerization, oxidation of the NS heterocyclic carbene to form the sulphoxide appears to have the opposite effect.

Dimerization mechanisms of heterocyclic carbenes

Publisher: Wiley

Date: 07-09-2004

DOI: 10.1002/POC.846

Understanding the influence of donor-acceptor diazo compounds on the catalyst efficiency of B(C6F5)3 towards carbene formation

Publisher: Wiley

Date: 27-01-2022

DOI: 10.1002/CHEM.202104376

Abstract: Diazo compounds have been largely used as carbene precursors for carbene transfer reactions in a variety of functionalization reactions. However, the ease of carbene generation from the corresponding diazo compounds depends upon the electron donating/withdrawing substituents either side of the diazo functionality. These groups strongly impact the ease of N 2 release. Recently, tris(pentafluorophenyl)borane [B(C 6 F 5 ) 3 ] has been shown to be an alternative transition metal‐free catalyst for carbene transfer reactions. Herein, a density functional theory (DFT) study on the generation of carbene species from α‐aryl α‐diazocarbonyl compounds using catalytic amounts of B(C 6 F 5 ) 3 is reported. The significant finding is that the efficiency of the catalyst depends directly on the nature of the substituents on both the aryl ring and the carbonyl group of the substrate. In some cases, the boron catalyst has negligible effect on the ease of the carbene formation, while in other cases there is a dramatic reduction in the activation energy of the reaction. This direct dependence is not commonly observed in catalysis and this finding opens the way for intelligent design of this and other similar catalytic reactions.

Rationalizing the different products in the reaction of N2 with three-coordinate MoL3 complexes

Publisher: Royal Society of Chemistry (RSC)

Date: 2007

DOI: 10.1039/B701050H

Abstract: The reaction of N2 with three-coordinate MoL3 complexes is known to give rise to different products, N-MoL3, L3Mo-N-MoL3 or Mo2L6, depending on the nature of the ligand L. The energetics of the different reaction pathways are compared for L = NH2, NMe2, N((i)Pr)Ar and N((t)Bu)Ar (Ar = 3,5-C6H3Me2) using density functional methods in order to rationalize the experimental results. Overall, the exothermicity of each reaction pathway decreases as the ligand size increases, largely due to the increased steric crowding in the products compared to reactants. In the absence of steric strain, the formation of the metal-metal bonded dimer, Mo2L6, is the most exothermic pathway but this reaction shows the greatest sensitivity to ligand size varying from significantly exothermic, -403 kJ mol(-1) for L = NMe2, to endothermic, +78 kJ mol(-1) for L = N((t)Bu)Ar. For all four ligands, formation of N-MoL3 via cleavage of the N2 bridged dimer intermediate, L3Mo-N-N-MoL3, is strongly exothermic. However, in the presence of excess reactant MoL3, formation of the single atom-bridged complex L3Mo-N-MoL3 from N-MoL3 + MoL3 is both thermodynamically and kinetically favoured for L = NMe2 and N((i)Pr)Ar, in agreement with experiment. In the case of L = N((t)Bu)Ar, the greater steric bulk of the (t)Bu group results in a much less exothermic reaction and a calculated barrier of 66 kJ mol(-1) to formation of the L3Mo-N-MoL3 dimer. Consequently, for this ligand, the energetically and kinetically favoured product, consistent with the experimental data, is the nitride complex L3Mo-N.

Oxidative Addition of the Imidazolium Cation to Zerovalent Ni, Pd, and Pt: A Combined Density Functional and Experimental Study

Publisher: American Chemical Society (ACS)

Date: 08-2001

DOI: 10.1021/JA010628P

Abstract: Oxidative addition of different imidazolium cations to zerovalent group 10 metals, to afford heterocyclic carbene complexes, has been investigated by both density functional theory (DFT) and experimental studies. The theoretical analysis shows that addition of imidazoliums to Pt(0) and Ni(0) is more exothermic than to Pd(0), and Ni(0) is predicted to react with a much lower barrier than either Pt(0) or Pd(0). Strongly basic supporting ligands on the metal, as well as cis-chelating ligands, increase the exothermicity of the reaction and also lower the activation barrier. The addition of 2-H imidazoliums is easier and more exothermic than addition of 2-alkylimidazoliums, and a halo-imidazolium is expected to further lower the barrier to oxidative addition and increase the exothermicity. The DFT results show that all three of the metals should be able to oxidatively add imidazolium cations under appropriate conditions. Experimental studies confirmed that oxidative addition is possible, and a number of Pt- and Pd-carbene complexes were prepared via oxidative addition of imidazolium salts to M(0) precursors. Most significantly, oxidative addition of 2-H azolium salts was found to readily occur, and the reaction of 1,3-dimethylimidazolium tetrafluoroborate with Pt(PPh(3))(2) and Pt(PCy(3))(2) affords [PtH(dmiy)(PPh(3))(2)]BF(4) (10) and [PtH(dmiy)(PCy(3))(2)]BF(4) (11), while reaction between 3,4-dimethylthiazolium tetrafluoroborate and Pt(PCy(3))(2) yields [PtH(dmty)(PCy(3))(2)]BF(4) (12) (dmiy = 1,3-dimethylimidazolin-2-ylidene, dmty = 3,4-dimethylthiazolin-2-ylidene). Addition of 2-iodo-1,3,4,5-tetramethylimidazolium tetrafluoroborate to Pt(PPh(3))(4) or Pd(dcype)(dba) yields [PtI(tmiy)(PPh(3))(2)]BF(4) (9) and [PdI(tmiy)(dcype)]BF(4) (14), respectively (tmiy = 1,3,4,5-tetramethylimidazolin-2-ylidene, dcype = 1,3-bis(dicyclohexylphosphino)ethane)). X-ray crystal structures are reported for complexes 9 and 11 (cis and trans). These studies clearly show for the first time that oxidative addition of imidazolium and thiazolium cations is possible, and the results are discussed in terms of the ramifications for catalysis in imidazolium-based ionic liquids with both carbene-based and non-carbene-based complexes.

A quantitative investigation of the transannular amine-ketone (N...C=O interaction in medium-sized heterocycles

Publisher: Elsevier BV

Date: 04-1997

DOI: 10.1016/S1093-3263(97)00019-3

Abstract: Leiomyomas are the most common benign tumours of the female genital tract, and almost always arise from the uterine myometrium. Although extrauterine leiomyomas are rare, they usually develop in sites such as the ovary, broad ligament, round ligament, cervix or abdominal wall. The broad ligament is the most common site of extrauterine leiomyoma involvement, and this unique clinical entity may prove to be a diagnostic or therapeutic challenge, particularly in patients with advanced endometriosis and distorted pelvic anatomy. Herein, we report the case of a large true broad ligament leiomyoma that was discovered during a total laparoscopic hysterectomy and bilateral salpingo-oophorectomy in a 47-year-old patient with stage IV endometriosis and a congenital left kidney and left ureter. This case highlights a rare occurrence of a true broad ligament leiomyoma, the challenges associated with preoperative diagnosis, and the laparoscopic approach to its management.

Theoretical Study of the Mechanism of CO and Acetylene Migratory Insertions into Pt–Cp* Bonds

Publisher: American Chemical Society (ACS)

Date: 24-04-2014

DOI: 10.1021/OM500273X

Computational Organic Chemistry

Publisher: Royal Society of Chemistry (RSC)

Date: 2004

DOI: 10.1039/B404044A

Density Functional Theory Study on the Mechanism of the Reductive Cleavage of CO₂ by a Bis-β-Diketoiminatediiron Dinitrogen Complex

Publisher: American Chemical Society (ACS)

Date: 11-08-2010

DOI: 10.1021/IC1005715

Abstract: Density functional theory has been used to analyze the detailed reaction mechanism for the reductive cleavage of CO(2) by a dinitrogen bridged bis-beta-diketoiminatediiron complex, L(tBu)Fe-N(2)-FeL(tBu) (I), recently reported by Holland and co-workers. A number of pathways have been investigated and the most likely mechanism correlates well with experimental evidence. A rationale has been provided for the binding of CO(2), the release of CO, and the ready formation of CO(3)(2-). Our results show that the insertion of CO(2) into the diiron complex is the rate determining step of the reductive cleavage reaction. An intramolecular reduction step from the reduced dinitrogen bridge is proposed which serves to increase the activation of CO(2). This is followed by an intersystem crossing from the septet to the nonet state which acts as a driving force for the subsequent release of CO. The overall reductive cleavage reaction is exergonic by 120 kJ/mol, and further reaction of the released CO with the starting diiron complex is also predicted to be strongly exergonic.

Subtle Balance of Ligand Steric Effects in Stille Transmetalation

Publisher: American Chemical Society (ACS)

Date: 11-09-2009

DOI: 10.1021/JA9007134

Abstract: Experimental results have previously suggested that the transmetalation step in the Stille reaction is hindered at one extreme by very bulky ligands L on the PdL(2) catalyst, yet at the other extreme, transmetalation is also found to be slow for small ligands. Our aim in this paper is to resolve this dilemma using computational chemistry and to show which ligand is best and why. With the use of density functional theory we show that the reason why L = P(t)Bu(3) retards transmetalation is because the bulky ligand hinders the coordination of the organostannane. On the other hand a small ligand such as L = PMe(3) leads to the formation of a very stable intermediate in the catalytic cycle which then requires a large activation energy for the transmetalation to proceed. The L = PPh(3) ligand appears to provide just the right balance in that it can readily coordinate the organostannane but avoids forming the very stable intermediate, and is thus the ligand of choice. L = PPh(2)Me is predicted to be the next best option, but L = PPhMe(2) is too small and forms an intermediate whose stability prevents further reaction in the transmetalation step. Our calculations are also able to account for the accelerating role of CsF in the transmetalation step of the Stille reaction. Finally, this work demonstrates the importance of taking into account the steric properties of the full ligand in theoretical studies of such reactions, rather than using small model phosphines.

Tuning the Laplaza-Cummins 3-coordinate M[N(R)Ph]3 catalyst to activate and cleave CO2

Publisher: Royal Society of Chemistry (RSC)

Date: 2011

DOI: 10.1039/C1DT10026B

Abstract: The Laplaza-Cummins catalyst L(3)Mo (L = N(R)Ar), is experimentally inactive towards carbon dioxide. Previous theoretical analysis identified the cause for this inactivity and suggested that a switch to a d(2) transition metal may induce activity towards the inert CO(2) molecule. In this manuscript we have tested this hypothesis by altering the central metal to Ta, Nb or V. Our calculations suggest that the tantalum analogue, TaL(3), will successfully bind to CO(2) in a mononuclear η(2) arrangement and, importantly, will strongly activate one C-O bond to a point where spontaneous C-O cleavage occurs. This prediction of a strongly exothermic reaction takes into consideration the initial barrier to formation, spin crossings, ligand bulk and even the choice of density functional in the calculations. The Nb analogue will likely coordinate CO(2) but reaction may not proceed further. In contrast, the V analogue faces an initial coordination barrier and is not expected to be sufficiently active to coordinate CO(2) to the triamide catalyst. A similar scenario exists for mixed metal interactions involving a d(2) and d(4) combination in a bridging dinuclear arrangement.

Cu-Catalyzed Fluorination of Diaryliodonium Salts with KF

Publisher: American Chemical Society (ACS)

Date: 24-09-2013

DOI: 10.1021/OL4025716

Modifiable factors associated with depression and anxiety in multiple sclerosis

Publisher: Hindawi Limited

Date: 24-06-2019

DOI: 10.1111/ANE.13132

Abstract: Modifiable lifestyle factors are implicated in multiple sclerosis (MS) symptoms but their role in mood is unclear. This study aimed to investigate associations between lifestyle and depression and anxiety in Australian participants with MS. Self-reported data from the Australian Multiple Sclerosis Longitudinal Study included the Hospital Anxiety and Depression Scale (HADS) and lifestyle measurements from 1500 participants. SNAP score (range 0-5) was the sum of non-smoking, sufficient fruit/vegetable intake, non-hazardous alcohol consumption, sufficient physical activity and healthy BMI. Analyses by log-binomial and linear regression were adjusted for confounding. Symptoms of depression and anxiety were prevalent in 27% and 40%, respectively 20% had both. Mean SNAP score was 2.7/5 only 3% met all healthy lifestyle recommendations. Only 10% reported adequate fruit/vegetable intake, and 22% reported a combination of unhealthy BMI, inadequate physical activity and inadequate nutrition. A healthier SNAP score was associated with lower depression prevalence (adjusted prevalence ratio 0.83 [95% CI 0.75, 0.92] per unit increase) and depression severity (adjusted β-0.44 [95% CI -0.64, -0.24]), but not with anxiety. Modifiable lifestyle factors are associated with lower frequency and severity of depression, but not anxiety, in Australian people with multiple sclerosis. The associations between a healthier SNAP score and lower depression are likely bi-directional. SNAP risk factor prevalence and co-occurrence, especially inadequate nutrition and low physical activity, were high among Australians with MS.

Insight into the Mechanism of R−R Reductive Elimination from the Six-Coordinate d⁶ Complexes L₂Pt(R)₄ (R = vinyl, Me)

Publisher: American Chemical Society (ACS)

Date: 05-01-2011

DOI: 10.1021/OM1005512

Different Selectivities in the Insertions into C(sp² )−H Bonds: Benzofulvenes by Dual Gold Catalysis Competition Experiments

Publisher: Wiley

Date: 28-06-2018

DOI: 10.1002/CHEM.201801031

Abstract: An unprecedented, often almost quantitative access to tricyclic aromatic compounds by dual gold catalysis was developed. This synthetic route expands the scope of benzofulvene derivatives through a C(sp

Economical treatments of relativistic effects and electron correlation in WH6

Publisher: Wiley

Date: 15-11-1998

DOI: 10.1002/(SICI)1096-987X(19981115)19:14<1604::AID-JCC6>3.0.CO;2-N

Computational Study of Carbostannylation Implicating Bimetallic Catalysis Involving “Au^I–Vinyl–Pd^II” Species

Publisher: American Chemical Society (ACS)

Date: 12-02-2014

DOI: 10.1021/CS400836V

Proton supplier role of binuclear gold complexes in promoting hydrofunctionalisation of nonactivated alkenes

Publisher: Royal Society of Chemistry (RSC)

Date: 2019

DOI: 10.1039/C8CY02482K

Abstract: PR 3 AuOTf-Catalyzed hydrofunctionalisation of nonactivated alkenes using acetic acid and phenol was found to take place via a binuclear mechanism.

Structural and electronic characterisation of the organometallic distonic ion (C6H6)Fe+(p-C6H4)

Publisher: Elsevier BV

Date: 07-2000

DOI: 10.1016/S1387-3806(00)00227-X

Computational organic chemistry

Publisher: Royal Society of Chemistry (RSC)

Date: 2006

DOI: 10.1039/B518099F

Associative Versus Dissociative Binding of CO to 4d Transistion Metal Trimers: A Density Functional Study

Publisher: Wiley

Date: 04-04-2008

DOI: 10.1002/JCC.20912

Abstract: Density functional calculations were performed to determine equilibrium geometrical structures, transition states and relative energies for M(3) clusters (M = Nb, Mo, Tc, Ru, Rh, Pd, Ag) reacting with CO, leading to proposed reaction pathways. For the Nb(3), Mo(3), and Tc(3) clusters, the lowest energy structure correlates to dissociated CO, with the C and O atoms bound on opposite sides of the metal triangle. For all other trimers, the lowest energy structures maintain the CO moiety. In the case of Pd(3) and Ag(3) the dissociated geometries lie higher in energy than the sum of the separated reactants. In most cases, several multiplicities were found to be similar in energy and for Mo(3)CO and Pd(3)CO singlet-triplet minimum energy crossing points were identified. In the case of Rh(3)CO, minimum energy crossing points for the doublet, quartet, and sextet reaction pathways were determined and compared. The electron densities of pertinent M(3)CO species were investigated using Natural Bond Order calculations. It was found that the effect of the metal trimer on the energy of the pure p-type pi* antibonding orbital of carbon monoxide directly correlates with the occurrence of CO dissociation.

Ethylene Trimerisation with Cr-PNP Catalysts: A Theoretical Benchmarking Study and Assessment of Catalyst Oxidation State

Publisher: CSIRO Publishing

Date: 2014

DOI: 10.1071/CH14436

Abstract: A model for the homogeneous Cr-PNP (PNP = diphosphinoamine) ethylene trimerisation and tetramerisation catalyst system has been studied theoretically, with the aim of identifying suitable density functional theory methods for treatment of this catalyst, and evaluating the likely oxidation and spin states of the active species. Benchmarking studies involving high-level treatment reveal the difficulty of accurately calculating the thermochemistry of this system, and suggest that local density functionals, such as M06L, probably provide the best option. Density functional theory modelling of catalyst activation and the first steps of oligomerisation up until 1-hexene formation appears to favour a CrI–CrIII mechanism, involving spin surface crossing from sextet to quartet states.

Unprecedented C-H bond oxidative addition of the imidazolium cation to Pt-0: a combined density functional analysis and experimental study

Publisher: Royal Society of Chemistry (RSC)

Date: 2001

DOI: 10.1039/B009674L

Acyl radical addition to pyridine: multiorbital interactions

Publisher: Elsevier BV

Date: 09-2009

DOI: 10.1016/J.TET.2009.06.102

Phosphine-Scavenging Role of Gold(I) Complexes from Pd(P^tBu₃)₂ in the Bimetallic Catalysis of Carbostannylation of Alkynes

Publisher: American Chemical Society (ACS)

Date: 08-05-2017

DOI: 10.1021/ACS.ORGANOMET.7B00237

Factors Dictating Carbene Formation at (PNP)Ir

Publisher: American Chemical Society (ACS)

Date: 07-09-2010

DOI: 10.1021/OM100211A

Experimental and theoretical investigation into the gold-catalyzed reactivity of cyclopropenylmethyl acetates

Publisher: American Chemical Society (ACS)

Date: 28-09-2010

DOI: 10.1021/OL101862U

Abstract: Cyclopropenylmethyl acetates have been shown to undergo rapid and stereoselective gold catalyzed rearrangement to Z-acetoxydienes in high yield. DFT calculations have shown that while several reaction pathways can be envisaged only a single, ring-opening one operates.

Lanthanide(II) and -(III) porphyrinogens - Rational synthesis and derivatisation of mononuclear, alkali-metal-free lanthanide(II) and -(III) meso-octaalkylporphyrinogen complexes

Publisher: Wiley

Date: 05-2004

DOI: 10.1002/EJIC.200300965

Site-Selective C_sp³–C_sp/C_sp³–C_sp² Cross-Coupling Reactions Using Frustrated Lewis Pairs

Publisher: American Chemical Society (ACS)

Date: 15-03-2021

DOI: 10.1021/JACS.1C01622

Mechanistic Investigations of Cu-Catalyzed Fluorination of Diaryliodonium Salts: Elaborating the Cu^I/Cu^III Manifold in Copper Catalysis

Publisher: American Chemical Society (ACS)

Date: 22-09-2014

DOI: 10.1021/OM5007903

Breaking Chemistry's Strongest Bond: Can Three‐Coordinate [M{N(R)Ar}₃] Complexes Cleave Carbon Monoxide?

Publisher: Wiley

Date: 04-05-2007

DOI: 10.1002/CHEM.200601643

Abstract: The reaction pathway for the interaction of CO with three-coordinate TaIII, WIII and ReIII complexes (modelled on the experimental [M{N(tBu)Ar}3] system) has been explored by using density functional methods. Calculations show that CO binds without a barrier to [Re(NH2)3], forming the encounter complex [OC--Re(NH2)3], which is stabilized by approximately 280 kJ mol-1 relative to the reactants. The binding of [Ta(NH2)3] to the oxygen terminus of CO is inhibited by a barrier of only 20 kJ mol-1 and is followed by spontaneous cleavage of the C--O bond to form the products [C--Re(NH2)3] and [O--Ta(NH2)3]. The salient features of the potential energy surface are more favourable to CO cleavage than the analogous N2 cleavage by [Mo(NH2)3], which is less exothermic (335 vs. 467 kJ mol-1) and is impeded by a significant barrier (66 kJ mol-1). The ReIII/TaIII/CO system therefore appears to be an excellent candidate for cleaving the exceptionally strong C--O bond under mild laboratory conditions. The related WIII/TaIII dimer, which significantly weakens but does not cleave the CO bond, may be a suitable alternative when the chemistry is to be performed on activated CO rather than on the strongly bound oxide and carbide cleavage products.

On the selective cleavage of nitrous oxide by metal–amide complexes

Publisher: Royal Society of Chemistry (RSC)

Date: 2014

DOI: 10.1039/C3DT53062K

Abstract: The remarkable selective cleavage of nitrous oxide by metal–amide systems, involving a bimetallic mechanism, has been investigated using computational methodology and rationalized on the basis of the interplay of structural and bonding factors.

Nitrogen Activation via Three-Coordinate Molybdenum Complexes: Comparison of Density Functional Theory Performance with Wave Function Based Methods

Publisher: American Chemical Society (ACS)

Date: 13-07-2005

DOI: 10.1021/JP044217H

Abstract: Obtaining an accurate theoretical model for the activation of dinitrogen by three-coordinate molybdenum amide complexes (e.g. Mo(NH2)3) is difficult due to the interaction of various high- and low-spin open-shell complexes along the reaction coordinate which must be treated with comparable levels of accuracy in order to obtain reasonable potential energy surfaces. Density functional theory with present-day functionals is a popular choice in this situation however, the dinitrogen activation reaction energetics vary substantially with the choice of functional. An assessment of the reaction using specialized wave function based methods indicates that although current density functionals in general agree qualitatively on the mechanistic details of the reaction, a variety of high-level electron correlation methods (including CCSD(T), OD(T), CCSD(2), KS-CCSD(T), and spin-flip CCSD) provide a consistent but slightly different representation of the system.

Formation of Ethane from Mono-Methyl Palladium(II) Complexes

Publisher: American Chemical Society (ACS)

Date: 02-06-2014

DOI: 10.1021/JA412338K

Abstract: This article describes the high-yielding and selective oxidatively induced formation of ethane from mono-methyl palladium complexes. Mechanistic details of this reaction have been explored via both experiment and computation. On the basis of these studies, a mechanism involving methyl group transmetalation between Pd(II) and Pd(IV) interediates is proposed.

Acyl radical addition to benzene and related systems - A computational study

Publisher: Elsevier BV

Date: 09-2010

DOI: 10.1016/J.TET.2010.07.041

Bismuth(III)-catalysed hydroalkylation of styrene with acetylacetone: a DFT-Based mechanistic study

Publisher: Informa UK Limited

Date: 08-07-2022

DOI: 10.1080/00268976.2022.2093798

Pre-catalyst resting states: a kinetic, thermodynamic and quantum mechanical analyses of [PdCl2(2-oxazoline)2] complexes

Publisher: Royal Society of Chemistry (RSC)

Date: 2008

DOI: 10.1039/B801951G

Abstract: The treatment of cold ( approximately 3 degrees C) methanolic solutions of Li(2)PdCl(4) with two equivalents of 2-phenyl-2-oxazoline (Phox) results in the isolation of [PdCl(2)(Phox)(2)] (3). This complex undergoes remarkably slow isomerisation (CHCl(3)-d) at room temperature to a corresponding thermodynamic form. In addition to a theoretical treatment (DFT), the isomerisation behaviour has been analysed both kinetically and thermodynamically. These investigations lead to the conclusion that the initially formed (i.e. kinetic) isomer of 3 is the cis-form which undergoes conversion to the corresponding thermodynamic trans-form via a dissociative (D) mechanism involving loss of a Phox ligand. The activation parameters DeltaS(double dagger) and DeltaH(double dagger) are found to be +304 (+/-3) J K(-1) mol(-1) and +176 (+/-1) kJ mol(-1), respectively and indicate a high barrier to Pd-N bond cleavage under these conditions. The thermodynamic parameters show the expected endothermic nature of this process (+140 +/- 17 kJ mol(-1)) and a slight positive overall entropy (DeltaS degrees = +17 +/- 2 J K(-1) mol(-1)) this latter parameter is presumably due to the formation of the lower dipole moment trans-product when compared to the cis-isomer. Calculated (DFT) values of DeltaG(double dagger) and DeltaH(double dagger) are in excellent agreement to those found experimentally. Further theoretical investigation suggests that two 14-electron three-coordinate T-shaped transition states (i.e., [PdCl(2)(Phox)](double dagger)) are involved the form pre-disposed to yield the thermodynamic trans-product following re-attachment of the released oxazoline is found to be energetically favoured. The analogous alkyloxazoline system [PdCl(2)(Meox)(2)] (4: Meox = 2-methyl-2-oxazoline) has likewise been investigated. This material gives no indication of cis-trans isomerisation behaviour in solution (NMR) and is shown to exist (X-ray) in the trans-form in the solid-state (as do previously reported crystalline s les of 3). A DFT study of 4 reveals similar values of DeltaS(double dagger) and DeltaH(double dagger) if a D type mechanism were operating to rapidly convert cis- to trans-4. However, a significantly higher thermodynamic stability of the trans-isomer relative to the cis-form is revealed versus similar calculations of the Phox derivative 3. This suggests the possibility that (i) reactions of Meox with Li(2)PdCl(4) may lead directly to the trans-form of [PdCl(2)(Meox)(2)] or alternatively (ii) that alkyloxazoline complexes such as 4 may have a different, and presumably much more rapid, mechanism for isomerisation. The results are placed into the context that isomerisation behaviour, or lack thereof, could play a key preliminary role in later substrate modification. This is due to the fact that [PdX(2)(oxazoline)(2)] compounds are well-known (pre-)catalysts for C-C bond forming chemistry.

Computational organic chemistry

Publisher: Royal Society of Chemistry (RSC)

Date: 2003

DOI: 10.1039/B212014N

Cleavage of CO by Mo[N(R)Ar]₃ Complexes

Publisher: Wiley

Date: 31-07-2007

DOI: 10.1002/EJIC.200700304

Theoretical study of methyl-Pd-II N-heterocyclic silylene and germylene complexes: Comparisons to N-heterocyclic carbene reactivity

Publisher: American Chemical Society (ACS)

Date: 29-10-2002

DOI: 10.1021/OM020750C

Activation and cleavage of the N–O bond in dinuclear mixed-metal nitrosyl systems and comparative analysis of carbon monoxide, dinitrogen, and nitric oxideactivation

Publisher: Royal Society of Chemistry (RSC)

Date: 2009

DOI: 10.1039/B812568F

Abstract: The activation and scission of the N-O bond in nitric oxide using dinuclear mixed-metal species, comprising transition elements with d(3) and d(2) configurations and trisamide ligand systems, have been investigated by means of density functional calculations. The [Cr(iii)-V(iii)] system is analyzed in detail and, for comparative purposes, the [Mo(iii)-Nb(iii)], [W(iii)-Ta(iii)], and (mixed-row) [Mo(iii)-V(iii)] systems are also considered. The overall reaction and in idual intermediate steps are favourable for all systems, including the case where first row (Cr and V) metals are exclusively involved, a result that has not been observed for the related dinitrogen and carbon monoxide systems. In contrast to the cleavage of dinitrogen by three-coordinate Mo amide complexes where the dinuclear intermediate possesses a linear [Mo-NN-Mo] core, the [M-NO-M'] core must undergo significant bending in order to stabilize the dinuclear species sufficiently for the reaction to proceed beyond the formation of the nitrosyl encounter complex. A comparative bonding analysis of nitric oxide, dinitrogen and carbon monoxide activation is also presented. The overall results indicate that the pi interactions are the dominant factor in the bonding across the [M-L(1)L(2)-M'] (L(1)L(2) = N-O, N-N, C-O) moiety and, consequently, the activation of the L(1)-L(2) bond. These trends arise from the fact that the energy gaps between the pi orbitals on the metal and small molecule fragments are much more favourable than for the corresponding sigma orbitals. The pi energy gaps decrease in the order [NO < N(2) < CO] and consequently, for each in idual pi orbital interaction, the back donation between the metal and small molecule increases in the order [CO < N(2) < NO]. These results are in accord with previous findings suggesting that optimization of the pi interactions plays a central role in increasing the ability of these transition metal systems to activate and cleave small molecule bonds.

Theoretical investigation into the palladium-catalyzed silaboration of pyridines

Publisher: American Chemical Society (ACS)

Date: 07-02-2012

DOI: 10.1021/OM2008106

Theoretical evaluation of alternative pathways in the Stevens rearrangement

Publisher: CSIRO Publishing

Date: 1995

DOI: 10.1071/CH9951413

Abstract: Ab initio and semi-empirical molecular orbital theory has been used to explore the ion-pair and lithium-catalysed pathways in the Stevens rearrangement of an alkylammonium ylide to an amine. These pathways represent alternatives to the concerted and free radical mechanisms which we have previously studied. Solvation effects have been included via a polarizable continuum model. Finally, the calculations have been extended to a set of experimentally observable compounds. For the nine systems studied here, the stepwise free radical pathway is predicted in every case to be the favourable mechanism for the Stevens rearrangement. Single-point MP2/6-31G(d) calculations on fully optimized PM3 geometries are shown to provide a useful method of including electron correlation at low computational cost.

Connecting Binuclear Pd(III) and Mononuclear Pd(IV) Chemistry by Pd–Pd Bond Cleavage

Publisher: American Chemical Society (ACS)

Date: 17-07-2012

DOI: 10.1021/JA304401U

Abstract: Oxidation of binuclear Pd(II) complexes with PhICl(2) or PhI(OAc)(2) has previously been shown to afford binuclear Pd(III) complexes featuring a Pd-Pd bond. In contrast, oxidation of binuclear Pd(II) complexes with electrophilic trifluoromethylating ("CF(3)(+)") reagents has been reported to afford mononuclear Pd(IV) complexes. Herein, we report experimental and computational studies of the oxidation of a binuclear Pd(II) complex with "CF(3)(+)" reagents. These studies suggest that a mononuclear Pd(IV) complex is generated by an oxidation-fragmentation sequence proceeding via fragmentation of an initially formed, formally binuclear Pd(III), intermediate. The observation that binuclear Pd(III) and mononuclear Pd(IV) complexes are accessible in the same reactions offers an opportunity for understanding the role of nuclearity in both oxidation and subsequent C-X bond-forming reactions.

Theoretical Investigation into the Mechanism of Au(I)-Catalyzed Reaction of Alcohols with 1,5 Enynes

Publisher: American Chemical Society (ACS)

Date: 02-10-2012

DOI: 10.1021/JA308038Z

Abstract: Density functional theory has been used to investigate the reactions of 1,5 enynes with alcohols in the presence of a gold catalyst. We have compared the mechanism of the alcohol addition reaction for the enyne with that of the enyne where the carbon at position 3 is replaced with silicon. We find that different intermediates are present in both cases, and in the case of the silicon analogue, the intermediate that we find from the calculations is different from any that have previously been proposed in the literature. For the silicon analogue we have been able to rationalize the observed effects of alcohol concentration and nucleophilicity on the product distribution. For the carbon-based enyne we have shown why different products are observed depending on the substitution at position 3 of the enyne. Overall, we have provided for the first time a consistent explanation and rationalization of several different experiments that have been previously published in the literature. Our mechanism will assist in predicting the outcome of experimental reactions involving different alcohols, reagent concentrations, and substitution patterns of the 1,5 enynes.

Unprecedented C-H bond oxidative addition of the imidazolium cation to Pt-0: a combined density functional analysis and experimental study

Publisher: Royal Society of Chemistry (RSC)

Date: 2001

DOI: 10.1039/B009674L

Ligand rotation in [Ar(R)N](3)M-N-2-M '[N(R)Ar](3) (M, M ' = Mo-III, Nb-III; R = Pr-i and Bu-t) dimers

Publisher: Royal Society of Chemistry (RSC)

Date: 2005

DOI: 10.1039/B413766C

Abstract: Earlier calculations on the model N2-bridged dimer (micro-N2)-{Mo[NH2]3}2 revealed that ligand rotation away from a trigonal arrangement around the metal centres was energetically favourable resulting in a reversal of the singlet and triplet energies such that the singlet state was stabilized 13 kJ mol(-1) below the D(3d) triplet structure. These calculations, however, ignored the steric bulk of the amide ligands N(R)Ar (R =iPr and tBu, Ar = 3,5-C6H3Me2) which may prevent or limit the extent of ligand rotation. In order to investigate the consequences of steric crowding, density functional calculations using QM/MM techniques have been performed on the Mo(III)Mo(III) and Mo(III)Nb(III) intermediate dimer complexes (mu-N(2))-{Mo[N(R)Ar]3}2 and [Ar(R)N]3Mo-(mu-N2)-Nb[N(R)Ar]3 formed when three-coordinate Mo[N(R)Ar]3 and Nb[N(R)Ar]3 react with dinitrogen. The calculations indicate that ligand rotation away from a trigonal arrangement is energetically favourable for all of the ligands investigated and that the distortion is largely electronic in origin. However, the steric constraints of the bulky amide groups do play a role in determining the final orientation of the ligands, in particular, whether the ligands are rotated at one or both metal centres of the dimer. Analogous to the model system, QM/MM calculations predict a singlet ground state for the (mu-N2)-{Mo[N(R)Ar]3}2 dimers, a result which is seemingly at odds with the experimental triplet ground state found for the related (mu-N2)-{Mo[N(tBu)Ph]3}2 system. However, QM/MM calculations on the (mu-N2)-{Mo[N(tBu)Ph]3}2 dimer reveal that the singlet-triplet gap is nearly 20 kJ mol(-1) smaller and therefore this complex is expected to exhibit very different magnetic behaviour to the (mu-N2)-{Mo[N(R)Ar]3}2 system.

On the unprecedented level of dinitrogen activation in the calix[4]arene complex of Nb(iii)

Publisher: Royal Society of Chemistry (RSC)

Date: 2011

DOI: 10.1039/C1DT11091H

Abstract: The calix[4]arene niobium(III) complex ([L]Nb-N=N-Nb[L] where [L] = p-tert-butylcalix[4]arene), reported to bind N(2) in a μ(2)-linear dimeric capacity and to activate the N(2) triple bond to 1.39 Å, corresponding to the longest N(2) bond known in the end-on coordination mode, was subjected to a computational investigation involving both density functional and wavefunction based methods to establish the basis for the unprecedented level of activation. Replacement of the calix[4]arene ligand with hydroxide or methoxide ligands reveals that the organic backbone structure of the calix[4]arene ligand exerts negligible electronic influence over the metal centre, serving only to geometrically constrain the coordinating phenoxide groups. A fragment bonding analysis shows that metal-to-dinitrogen π* backbonding is the principal Nb-N interaction, providing a strong electronic basis for analogy with other well-characterised three- and four-coordinate complexes which bind N(2) end-on. While the calculated structure of the metallacalix[4]arene unit is reproduced with high accuracy, as is also the Nb-Nb separation, the calculated equilibrium geometry of the complex under a variety of conditions consistently indicates against a 1.39 Å activation of the N(2) bond. Instead, the calculated N-N distances fall within the range 1.26-1.30 Å, a result concordant with closely related three- and four-coordinate μ(2)-N(2) complexes as well as predictions derived from trends in N-N stretching frequency for a number of crystallographically characterized linear N(2) activators. A number of potential causes for this bond length discrepancy are explored.

Optimizing Small Molecule Activation and Cleavage in Three-Coordinate M[N(R)Ar]₃ Complexes

Publisher: American Chemical Society (ACS)

Date: 19-07-2006

DOI: 10.1021/IC051778U

Abstract: The sterically hindered, three-coordinate metal systems M[N(R)Ar]3 (R = tBu, iPr Ar = 3,5-C6H3Me2) are known to bind and activate a number of fundamental diatomic molecules via a [Ar(R)N]3M-L-L-M[N(R)Ar]3 dimer intermediate. To predict which metals are most suitable for activating and cleaving small molecules such as N(2), NO, CO, and CN(-), the M-L bond energies in the L-M(NH2)3 (L = O, N, C) model complexes were calculated for a wide range of metals, oxidation states, and dn (n = 2-6) configurations. The strongest M-O, M-N, and M-C bonds occurred for the d2, d3, and d4 metals, respectively, and for these d(n) configurations, the M-C and M-O bonds were calculated to be stronger than the M-N bonds. For isoelectronic metals, the bond strengths were found to increase both down a group and to the left of a period. Both the calculated N-N bond lengths and activation barriers for N2 bond cleavage in the (H2N)3M-N-N-M(NH2)3 intermediate dimers were shown to follow the trends in the M-N bond energies. The three-coordinate complexes of Ta(II), W(III), and Nb(II) are predicted to deliver more favorable N2 cleavage reactions than the experimentally known Mo(III) system and the Re(III)Ta(III) dimer, [Ar(R)N]3Re-CO-Ta[N(R)Ar]3, is thermodynamically best suited for cleaving CO.

Activation of CS₂ and CS by ML₃ Complexes

Publisher: American Chemical Society (ACS)

Date: 16-08-2008

DOI: 10.1021/JA800946E

Abstract: The aim of this study was to determine the best neutral ML3 metal complexes for activating and cleaving the multiple bonds in CS2 and CS. Current experimental results show that, so far, only one bond in CS2 can be cleaved, and that CS can be activated but the bond is not broken. In the work described in this paper, density functional theory calculations have been used to evaluate the effectiveness of different ML3 complexes to activate the C-S bonds in CS2 and CS, with M = Mo, Re, W, and Ta and L = NH2. These calculations show that the combination of Re and Ta in the L3Re/CS2/TaL3 complex would be the most promising system for the cleavage of both C-S bonds of CS2. The reaction to cleave both C-S bonds is predicted to be exothermic by about 700 kJ mol(-1) and to proceed in an almost barrierless fashion. In addition, we are able to rationalize why the breaking of the C-S bond in CS has not been observed experimentally with M = Mo: this reaction is strongly endothermic. There is a subtle interplay between charge transfer and pi back-donation, and it appears that the Mo-C and Mo-S bonds are not strong enough to compensate for the breaking of the C-S bond. Our results suggest that, instead, CS could be cleaved with ReL3 or, even better, with a combination of ReL3 and TaL3. Molecular orbitals and Mulliken charges have been used to help explain these trends and to make predictions about the most promising systems for future experimental exploration.

Influence of geometry on reductive elimination of hydrocarbyl-palladium-carbene complexes

Publisher: Royal Society of Chemistry (RSC)

Date: 2005

DOI: 10.1039/B417111J

Abstract: The influence of spectator ligand bite angle and the twist angle of the carbene on the reductive elimination of N-heterocyclic carbenes (NHCs) from palladium bis-phosphine complexes has been investigated using density functional theory. The spectator bite angle was found to have a significant influence on both the activation energy (E(act)) and the enthalpy of reaction. Widening of the bite angle was found to lower E(act) and increase the enthalpy of reaction. In contrast, rotation of the carbene with respect to the PdL(2) plane was found to have little influence on E(act). At carbene twist angles approaching 0 degrees however, relief of the increased steric strain provides a considerable driving force for the decomposition reaction.

Discovery of Redox-Promoted Brønsted Acid Catalysis in the Gold(III)-Catalyzed Annulation of Phenol and Cyclohexadiene

Publisher: American Chemical Society (ACS)

Date: 17-06-2022

DOI: 10.1021/ACSCATAL.2C01194

Kinetic and Density Functional Studies on Alkyl-Carbene Elimination from PdII Heterocyclic Carbene Complexes: A New Type of Reductive Elimination with Clear Implications for Catalysis

Publisher: American Chemical Society (ACS)

Date: 06-04-2001

DOI: 10.1021/JA003861G

Abstract: A number of new methyl-Pd(II) complexes of heterocyclic carbenes of the form [PdMe(tmiy)L(2)]BF(4) have been prepared, and their reaction behavior has been studied (tmiy = 1,3,4,5-tetramethylimidazolin-2-ylidene, L = cyclooctadiene (8), methyldiphenylphosphine (9), triphenyl phosphite (10), triphenylphosphine (11)). In common with other hydrocarbyl-M carbene complexes (M = Pd, Ni) the complexes are predisposed to a facile decomposition process. A detailed mechanism for the process and of the decomposition pathway followed is presented herein. All complexes decompose with first-order kinetics to yield 1,2,3,4,5-pentamethylimidazolium tetrafluoroborate and Pd(0) species. The kinetic investigations combined with density functional studies show that the complexes decompose via a mechanism of concerted reductive elimination of the methyl group and carbene. The reaction represents a new type of reductive elimination from transition metals and also represents a low-energy pathway to catalyst deactivation for catalysts based on heterocyclic carbenes. The theoretical studies indicate extensive involvement of the p(pi) orbital on the carbene carbon in the transition structure. Methods of stabilizing catalysts based on heterocyclic carbene complexes are suggested, and the possibility of involvement of carbene species during catalysis in ionic liquids is discussed.

The Mechanism of Ethylene Dimerization with the Ti(OR′)₄/AlR₃ Catalytic System: DFT Studies Comparing Metallacycle and Cossee Proposals

Publisher: American Chemical Society (ACS)

Date: 20-11-2013

DOI: 10.1021/CS4006875

Large basis set calculations on model zerovalent palladium systems

Publisher: American Chemical Society (ACS)

Date: 09-1995

DOI: 10.1021/J100039A019

Mixing of electronic states in molybdenum complexes involved in nitrogen activation

Publisher: Elsevier BV

Date: 05-2006

DOI: 10.1016/J.CHEMPHYS.2006.01.013

Mechanistic Studies of Ligand Fluxionality in [M(η⁵-Cp)(η¹-Cp)(L)₂]ⁿ

Publisher: American Chemical Society (ACS)

Date: 04-03-2009

DOI: 10.1021/JP810032A

Abstract: Density functional theory has been used to provide a thorough investigation of the mechanistic factors affecting Cp ligand fluxionality in a series of organometallic complexes, [M(eta(5)-Cp)(eta(1)-Cp)(L)(2)](n), involving different metals, different oxidation states, and different ligands. Excellent agreement with experiment for the barrier heights for the 1,5-shift were obtained for the complexes [Fe(eta(5)-Cp*)(eta(1)-Cp)(CO)(2)] and [Fe(eta(5)-Cp)(eta(1)-Cp)(CO)(2)]. For the range of complexes studied, the barriers have been successfully rationalized in terms of hyperconjugation, metal-Cp bond strength, and steric effects. In addition, the eta(1)-eta(5) interconversion of the Cp binding mode is shown to be a high-energy process, consistent with experimental observations. The L substitution reactions by eta(1)-Cp are quite sensitive to the nature of the metal center and ancillary ligand. A detailed theoretical explanation of the factors involved in all of these transformations is provided.

University Of Tasmania

Location: Australia

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Discovery Projects - Grant ID: DP120101540

Start Date: 2012

End Date: 12-2015

Amount: $290,000.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP0663045

Start Date: 2006

End Date: 01-2009

Amount: $460,000.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP0342577

Start Date: 2003

End Date: 12-2005

Amount: $255,000.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP0986529

Start Date: 2009

End Date: 12-2011

Amount: $330,000.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP0208832

Start Date: 11-2002

End Date: 12-2004

Amount: $245,000.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP0664792

Start Date: 2006

End Date: 03-2010

Amount: $240,000.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP120101937

Start Date: 2012

End Date: 06-2017

Amount: $410,000.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP180100904

Start Date: 06-2018

End Date: 06-2024

Amount: $381,855.00

Funder: Australian Research Council

Linkage Projects - Grant ID: LP120200241

Start Date: 09-2012

End Date: 06-2018

Amount: $340,000.00

Funder: Australian Research Council

Linkage Projects - Grant ID: LP0453774

Start Date: 2004

End Date: 06-2007

Amount: $178,000.00

Funder: Australian Research Council

Linkage Infrastructure, Equipment And Facilities - Grant ID: LE0239176

Start Date: 2001

End Date: 12-2002

Amount: $675,000.00

Funder: Australian Research Council

Linkage Projects - Grant ID: LP0882355

Start Date: 03-2008

End Date: 05-2011

Amount: $160,000.00

Funder: Australian Research Council