Decarbonylation of Aliphatic Aldehydes by a Tp(Me2)Ir(III) Metallacyclopentadiene

The Ir(III) compound Tp(Me2)Ir[C(CO2Me)= C(CO2Me)C(CO2Me)=C(CO2Me)(OH2) (I) reacts thermally with aliphatic aldehydes RC(0)H (R = Me, Bu-t) to lead to the decarbonylation products Tp(Me2)Ir[C(CO2Me)=C-(CO2Me)C(CO2Me)=C(CO2Me)](CO) (2) and RH. In turn, formaldehyde reacts with 1, yielding a product resulting from the hydrogenation of one of the double bonds of the iridacycle. Theoretical calculations reveal the role of the metallacycle as a shuttle for the transfer of the aldehyde H atom. Under photochemical (UV) irradiation, the decarbonylation reaction becomes catalytic for a variety of aliphatic aldehydes.