Synthesis of a novel ruthenium(ІІ) complex and its unique behaviors in enzymatic dynamic kinetic resolution of secondary alcohols

A cyclopentadienyl benzoyl ruthenium(ІІ) complex 3 was first prepared as an efficient catalyst in Candida Antarctica lipase B (CALB) mediated dynamic kinetic resolution (DKR) of secondary alcohols. With the aid of this ruthenium complex 3, (S)-1-phenylethanol was completely racemized within 25 min, and in combination with CALB, series of secondary alcohols bearing various functional groups were resolved in an efficient DKR manner. A detailed mechanism involving the C–H bond activation was presented for the formation of complex 3 by capturing the crucial intermediate in this pathway. Related mechanistic studies were carried out to illustrate this type of DKR catalyst is based on the racemization of secondary alcohols. The novelty of its structure, its unique catalytic behavior as well as its wide scope of application of various substrates and its higher efficiency make complex 3 as an important alternative to those complexes, which are commonly used in DKR process.