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