Annulated N-Heterocyclic Carbene Ligands Derived from 2-Methylaminopiperidine: Their Complexes and Catalytic Applications

A new type of carbene precursor, 1,5,6,7,8,8a-hexahydroimidazo[1,5-a]pyridine (1), has been prepared from 2-(aminomethyl)piperidine and N,N-dimethylformamide dimethylacetal. The reactions of three imidazolidinium salts with [Rh(acac)(COD)] and [Ir(μ-OMe)(COD)]2 were found to afford rhodium and iridium complexes of N-heterocyclic carbenes, respectively. These complexes have been tested as catalysts in the transfer hydrogenation of cyclohexanone and acetophenone using 2-propanol as hydrogen source.