Synthesis of New Iridium N-Heterocyclic Carbene Complexes Bearing a Functionalized Cp* Ligand and Their High Catalytic Activities in the Oppenauer-Type Oxidation of Alcohol

Abstract

The new iridium N-heterocyclic carbene complexes Cp*NIr(IMeMe)Cl2 and Cp*NIr(IMe)Cl2 (Cp*N = η5-1-[2-(dimethylamino)ethyl]-2,3,4,5-tetramethylcyclopentadienyl; IMeMe = 1,3,4,5-tetramethylimidazol-2-ylidene; IMe = 1,3-dimethylimidazol-2-ylidene) have been synthesized by reaction of η5:η1-Cp*NIrCl2 with silver(I) carbene complexes or a free carbene. The catalytic systems using new iridium carbene complexes as a catalyst precursor and AgOTf showed high catalytic activities in Oppenauer-type oxidation of alcohol and were applicable to oxidations of acid-sensitive alcohols that had been hard to oxidize by using [Cp*Ir(IMeMe)(MeCN)2][OTf]2.