Reactivity of Me-pma RhI and IrI Complexes upon Deprotonation and Their Application in Catalytic Carbene Carbonylation Reactions

Dehydrogenative oxidation of amines is a relevant process in metal-mediated catalysis, with the amines being either substrates or ligands. Transformation of amine- into imine-type ligands in the coordination sphere of a transition metal can be an important catalyst activation process. The behaviour of secondary pyridin-2-ylmethanamine (pma) ligands in the corresponding rhodium and iridium complexes upon NH deprotonation varies, depending on a number of factors. In this paper the behaviour of the Me-pma ligand [Me-pma = N-methyl-1-(pyridin-2-yl)methanamine] bound to [Rh(cod)]+ and [Ir(cod)]+ was studied. Whereas the iridium amido complex could be obtained upon NH deprotonation, the rhodium complex instantaneously disproportionated into a free pma ligand and an unusual dinuclear complex, adopting a structure with two RhI metal centres hosted by a dianionic (pma-2H)2– ligand, and with the ligand coordinating to Rh2 as an “aza-allyl” fragment. The study gives further proof for the effect of pyridine ligation on the previously observed charge-transfer from the ligand to the metal. Furthermore, the catalytic activity of both the Ir and the Rh species with Me-pma in carbene carbonylation reactions to generate ketenes was studied.