Electronic tuning of the PNNP ligand for the asymmetric cyclopropanation of olefins catalysed by [RuCl(PNNP)]+

Cationic ruthenium complexes of the type RuCl(L)(PNNP)]⁺ (L=OEt₂, OH₂), where PNNP is the CF₃-subsituted PNNP ligand N,N′-biso-(bis(4-trifluoromethylphenyl)phosphino)benzylidene]-(1S,2S)-diaminocyclohexane 1b, catalyse the asymmetric cyclopropanation of styrene, α-Me-styrene, and 1-octene with ethyl diazoacetate. These complexes are more active and give higher cis- and enantioselectivities than their analogues containing the unsubstituted ligand 1a. Thus, RuCl(OEt₂)(1b)]PF₆ cyclopropanates α-Me-styrene with 85% cis selectivity and 86% ee in 94% isolated yield.