Conformationally Flexible Biphenyl-phosphane Ligands for Ru-Catalyzed Enantioselective Hydrogenation

Abstract

Stereomutation of a BIPHEP/RuCl₂ /diamine complex (shown schematically) is possible because of the conformational flexibilty of BIPHEP ligands. The result is an asymmetric activation in the Ru-catalyzed hydrogenation of carbonyl compounds to optically active alcohols. Whereas a racemic BINAP/RuCl₂ complex with a chiral diamine activator gives a 1:1 mixture of two diastereomers, unequal amounts of the diastereomers can be produced from a BIPHEP/RuCl₂ complex and a chiral diamine. Ar=3,5-dimethylphenyl, BINAP=2,2'-bis(diphenylphosphanyl)-1,1'-binaphthyl, BIPHEP=2,2'-bis(diarylphosphanyl)biphenyl.