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(u-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.