A new optically pure half-sandwich Cp-Ru diphosphine complex with a chiral metal centre, (S)-Ru(eta 5-C5H5)(EPHOS)Cl [EPHOS is (+)-(1R,2S)-2-[(diphenylphosphino)methylamino]-1-phenylpropyl diphenylphosphinite].

The crystal structure of the title compound, chloro(eta(5)-cyclopentadienyl)[(1R,2S)-2-[(diphenylphosphino)methylamino]-1-phenylpropyl diphenylphosphinite-kappa(2)P,P']ruthenium(II), [Ru(C(5)H(5))Cl(C(34)H(33)NOP(2))], is reported. The pseudo-octahedral complex is chiral and the configuration at the Ru atom is S. The seven-membered metallacycle adopts a boat-like conformation.