4.3 Proposed mechanism
Based on the observations, a stepwise mechanism for the phase transfer hydrogenation of acetophenone with aqueous formate as hydrogen source and Ru-TsDPEN catalyst under an external electric field is proposed in Scheme 1. The cationic Ru complex 2 is generated by removal of chloride after compound 1 dissolves in 1-butanol. Following the formation, species 2 undergoes electromigration to the interface where a hydride is transferred to 2 from a formate to generate catalyst 3 , with the release of CO2.26 Instead of transferring both hydrogen to the substrate concertedly,31 only the hydride on Ru-H in catalyst 3 is transferred to acetophenone with the proton on the NH2 moiety retained,37 resulting in the regeneration of species2 and the formation of the corresponding alkoxide intermediate due to the stabilization of hydrogen bonding by water.37 Finally, the alkoxide picks up a proton from water to form the product,37 and the generated hydroxide further reacts with CO2 to form bicarbonate as observed in our previous study.25