Aluminium-ligand cooperation promotes selective dehydrogenation of formic acid to H-2 and CO2

Herein, we report that molecular aluminium complexes of the bis(imino) pyridine ligand, ((I2P2-)-I-Ph) Al(THF) X, X = H (1), CH3 (2), promote selective dehydrogenation of formic acid to H-2 and CO2 with an initial turnover frequency of 5200 turnovers per hour. Low-temperature reactions show that reaction of 1 with HCOOH affords a complex that is protonated three times: twice on the (I2P2-)-I-Ph ligand and once to liberate H-2 or CH4 from the Al-hydride or Al-methyl, respectively. We demonstrate that in the absence of protons, insertion of CO2 into the Al-hydride bond of 1 is facile and produces an Al-formate. Upon addition of protons, liberation of CO2 from the Al-formate complex affords an Al-hydride. Deuterium labelling studies and the solvent dependence of the reaction indicate that outer sphere beta-hydride abstraction supported by metal-ligand cooperative hydrogen bonding is a likely mechanism for the C-H bond cleavage.