Bulky N-Heterocyclic Carbene IPr* in Selected Organo- and Transition Metal-Mediated Catalytic Applications

A series of studies were conducted to probe the stability and reactivity of a very sterically encumbered N-heterocyclic carbene. The X-ray structure of the NHC IPr* (IPr* = 1,3-bis(2,6-bis(diphenylmethyl)-4-methylphenyl)imidazol-2-ylidene) was determined. IPr* was used as an organocatalyst in transesterification reactions. Steric and electronic parameters characterizing IPr* were determined via the synthesis of a nickel-carbonyl complex, [Ni(CO)(3)(IPr*)]. A related complex, [(Cp*)Ru(IPr*)Cl) (Cp* = eta(5)-C5Me5), was prepared and characterized by X-ray crystallography, and its catalytic performance in the racemization of chiral alcohols is reported. The catalytic performance of the NHC and of its transition metal derivatives permit establishing the standing of this uniquely bulky member among the NHC family.