Taming a monomeric [Cu(η-CH)] complex with silylene.

Previous theoretical and experimental endeavors suggested that [Cu(CH)] prefers the η/η mode over the η mode due to the augmented repulsion between the benzene ring and metal d-electrons. Nevertheless, the use of silylene as a neutral ligand has led to the isolation of the first monomeric copper cation, [{PhC(NBu)SiN(SiMe)}Cu(η-CH)][SbF] (), where a copper atom is bound to the benzene ring in an unsupported η fashion. However, the use of IPr (1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) in place of silylene results in the formation of [IPr·Cu(η-CH)][SbF] (), where the copper atom is bound to the benzene ring in the η mode. The discrepancy in hapticities is also reflected when hexamethylbenzene is employed as the arene ring. The silylene supported copper cation continues to bind in the η mode in while the NHC copper cation displays an η bonding mode in . DFT calculations are carried out to understand how the use of silylene led to the η binding mode and why IPr afforded the η binding mode.