N‐Heterocyclic Carbene Functionalized Iridium Phosphinidene Complex [Cp*(NHC)IrPMes*]: Comparison of Phosphinidene, Imido, and Carbene Complexes

NHC ligands versus cyclopentadienyls and phosphines as spectator ligands in organometallic catalysis

“…Meyer and coworkers [37] have argued that NHCs are Ôfair p-acceptorsÕ even with such relatively weakly p-basic metals as Cu(I), Ag(I) and Au(I), although Lammertsma and coworkers [38] have argued that the NHC is a weak p-acceptor even for a much more p-basic Ir(I) fragment. The difference may only be one of rhetorical emphasis but further work is clearly needed.…”

New tripodal N-heterocyclic carbene chelators for small molecule activation

“…In general, there is a lack of rigorous theoretical studies on metal NHC complexes, especially on the electronic nature of metal-carbene bonds. Nevertheless, several studies suggest various degrees of p-bonding in transition metal NHC complexes [37,38]. We applied DFT computational methods to thoroughly study the electronic structures of the TIME Me group 11 metal complexes 12-14 and related late metal NHC complexes [29].…”

Sterically induced differences in N-heterocyclic carbene transition metal complexes

“…There is only limitedbackbonding observed in transition metal NHC complexes precisely because the receiving p-orbital on carbon is already sufficiently filled with -electron density from the nitrogen lone pairs. Theacceptor strength of NHC is believed to be rather low [18], although it is no longer thought to be negligible [19]. It is well known that despite the excellent -donicity of NHC, excess of free NHC added to transition metal NHC complexes does not result in a bonding interaction between the lone pair of the singlet carbene and the p-orbital of the coordinated NHC.…”