Bulky N-Heterocyclic CarbeneIPr* in Selected Organo- and Transition Metal-Mediated Catalytic Applications.

A series of studies were conducted to probe the stabilityand 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 transesterificationreactions. Steric and electronic parameters characterizing IPr* weredetermined via the synthesis of a nickel-carbonyl complex, [Ni(CO)3(IPr*)]. A related complex, [(Cp*)Ru(IPr*)Cl] (Cp* = η5-C5Me5), was prepared and characterizedby X-ray crystallography, and its catalytic performance in the racemizationof chiral alcohols is reported. The catalytic performance of the NHCand of its transition metal derivatives permit establishing the standingof this uniquely bulky member among the NHC family. [ABSTRACT FROM AUTHOR]