Theoretical rationalisation for the mechanism of N-heterocyclic carbene-halide reductive elimination at Cu^III, Ag^III and Au^III

Abstract

A dichotomy in carbon versus bromide reductive elimination in CuIII–NHC complexes is rationalized by computational methods (DFT).

Phosphine-Scavenging Role of Gold(I) Complexes from Pd(PtBu3)2 in the Bimetallic Catalysis of Carbostannylation of Alkynes

“…It follows that Pd­(P t Bu 3 ) 2 is a stronger Lewis base than other substrates, as is evident from the fact that Pd­(P t Bu 3 ) 2 possesses a higher-lying HOMO with an energy level of −4.00 eV; the HOMO energy levels for the vinylstannane and the alkyne are calculated to be lower in energy (−6.92 and −7.85 eV, respectively). The antibonding character of the HOMO of the linear transition-metal complexes with d 10 configuration causes these complexes to be basic (Figure b) . However, this basicity is affected by the nature of the L ligands.…”

N-Heterocyclic Carbene Adducts of Main Group Elements and Their Use as Ligands in Transition Metal Chemistry

“… It is interesting to note that the reverse reaction occasionally afforded 2-halogenoimidazolium salts by reductive elimination for NHC metal complexes, and for instance [(IMes)­I]­I 3 was isolated by thermal decomposition of [(η 5 -C 5 H 5 )­Co­(IMes)­I]­I 3 , whereas [(IDipp)­I]­I 3 , [(IDipp)­Br]­OTf, and [(IDipp)­Cl]­SbF 6 were isolated from the copper­(I) complex [(IDipp)­CuX] (X = I, Br, Cl) in the presence of Selectfluor (1-chloromethyl-4-fluoro-1,4-diazoniabicyclo[2.2.2]­octane bis­(tetrafluoroborate)) as an oxidant . It was suggested that these reactions proceed through oxidation of Cu­(I) to Cu­(II) species followed by C carbene –halogen reductive elimination. , …”

“…905 It was suggested that these reactions proceed through oxidation of Cu(I) to Cu(II) species followed by C carbene −halogen reductive elimination. 905,906…”

High-Oxidation-State 3d Metal (Ti–Cu) Complexes withN-Heterocyclic Carbene Ligation

“…This difference could be due to the different electronic nature of the ancillary ligand, as a study by Willans, Ariafard, and Fairlamb on the C(carbene)−Br reductive elimination from the copper(III) species [trans-(IMe 2 H 2 )CuBr 2 X] + (210, X = benzyl, Me, vinyl, Ph, CF 3 , CN, I, F, Br, and Cl) indicated that the stronger σdonating nature of the X ligands results in higher activation energies of the reductive elimination step. 373 In addition to the aforementioned studies, copper(III) species were also implicated as intermediates in the formation of bis(imidazolium) salts in the reactions of (1-pyridinylimidazol-2-ylidene)silver(I) bromide with copper(II) dibromide (Scheme 81). 374 Willans et al found that the equimolar reaction of (1-pyridinyl-3-allylimidazol-2-ylidene)silver(I) bromide with copper(II) dibromide produced the copper(II)− NHC complex 176 in good yield, whereas changing the molar ratio into 1:2 suppressed the isolation of 176 and resulted in the formation of the 2-bromo-1-pyridinyl-3-allylimidazolium salt (Scheme 81).…”

“…The reluctance of the (NHC)­copper­(III) species 209 to undergo C–X reductive elimination forms a stark contrast to the facile reductive elimination from 207 . This difference could be due to the different electronic nature of the ancillary ligand, as a study by Willans, Ariafard, and Fairlamb on the C­(carbene)–Br reductive elimination from the copper­(III) species [ trans -(IMe 2 H 2 )­CuBr 2 X] + ( 210 , X = benzyl, Me, vinyl, Ph, CF 3 , CN, I, F, Br, and Cl) indicated that the stronger σ-donating nature of the X ligands results in higher activation energies of the reductive elimination step …”