Synthesis of a series of iridium complexes bearing substituted 2-pyridonates and their catalytic performance for acceptorless dehydrogenation of alcohols under neutral conditions

A series of Cp*Ir complexes bearing 5- and 4,5-substituted 2-pyridonate ligands have been synthesized and their catalytic performance for acceptorless dehydrogenation of alcohols has been investigated under neutral conditions. Electron-withdrawing groups such as methoxycarbonyl, trifluoromethyl, cyano, and nitro groups at the 5-position promoted the acceptorless dehydrogenation of 1-phenylethanol, whereas electron-donating methyl group at the 5-position retarded the reaction. Furthermore, introduction of methyl group at the 4-position improved the catalytic performance. Thus, Cp*Ir(5-trifluoromethyl-4-methyl-2-pyridonate)Cl (2bc) exhibited the highest catalytic performance among the complexes examined, and also showed good catalytic performance for acceptorless dehydrogenation of primary alcohols.