N-Heterocyclic carbene (NHC)–copper-catalysed transformations of carbon dioxide

Abstract

This minireview gives an overview of the chemical transformations of carbon dioxide (CO 2 ) catalysed by N-heterocyclic carbene (NHC)-copper complexes. NHC-copper complexes can serve as excellent catalysts for the carboxylation of various substrates with CO 2 and the reduction of CO 2 to CO or formic acid derivatives. In addition, NHC ligands enable the isolation of structurally characterisable key reaction intermediates, thus helping in understanding the mechanistic details of the catalytic processes. The related reactions catalysed by other metal complexes with NHC ligands are also briefly described.

Self-Assembly Fabrication of Hollow Mesoporous Silica@Co–Al Layered Double Hydroxide@Graphene and Application in Toxic Effluents Elimination

“…The molecular structure of the Λ-mer enantiomer of 1 is shown alongside eqn (1) (the asymmetric unit contains both Δ-mer and Λ-mer enantiomers). The molecule is isostructural with Ti(L) 3 and Y(L) 3 , previously reported by our group. 21,22 The Sc centre lies in a pseudo-octahedral environment, coordinated by three bidentate ligands in a merconformation.…”

“…2.036(2) and 2.046(2) Å). The structure exhibits similar long trans NHC-M distances to those in Y(L) 3 and Ti(L) 3 18,23 However, the M-C bond of 2.495(3) Å for the carbene trans to the alkoxide in 1 is the longest Sc-NHC distance yet reported, suggesting lability. 18,24,25 To investigate the potential for the Sc-NHC combination to engage in FLP-type behaviour, reactions of 1 with CO 2 and CS 2 were investigated.…”

“…3,4 Carbon disulfide (CS 2 ) is isoelectronic with CO 2 and has a more electrophilic carbon centre due to the weaker π-donor ability of the softer S, and is often studied as a comparator for CO 2 .…”

“…9 Frustrated Lewis pair (FLPs) systems are combinations of Lewis acids and Lewis bases that are prevented from reacting together by steric congestion. These have been used to activate CO 2 , for example, Stephan used B(C 6 F 5 ) 3 and PtBu 3 to trap CO 2 (C in Chart 1). 10 Such activation of CO 2 using FLPs has allowed subsequent reduction to methanol and methane.…”

“…10 Such activation of CO 2 using FLPs has allowed subsequent reduction to methanol and methane. 11,12 There are few, but an increasing number, of transition metal FLP type systems which can activate CO 2 3 1 in a 67% yield, eqn (1). The 1 H NMR spectrum of 1 at room temperature shows one set of broad ligand resonances which would indicate either C 3 symmetry in solution or that a fluxional process between free and bound carbenes is occurring on the NMR timescale.…”