The formation of [{(η-ring)M(Aa)}3](BF4)3 trimers [(η-ring)M=(η5-C5Me5)Rh, (η5-C5Me5)Ir, (η6-p-MeC6H4iPr)Ru; Aa = α-amino acidate, one cation shown schematically] takes place by chiral self-recognition, the RMRMRM or SMSMSM trimers are equally configurated at the metal centres and are the only diastereomers detected. The equilibrium constant for the diastereomerisation process between both isomers depends on the solvent, amino acidate, and metal. The trimers catalyse the reduction of unsaturated aldehydes to unsaturated alcohols and the reduction of acetophenone to 2-phenylethanol with up to 75 % ee.

We thank the Direccion General de Investigacion Cientifica y Tecnica for financial support (GrantPB96/0845). F.J. is grateful to IBERDROLA S.A. for sponsoring A.K. acknowledges the travel grant of the European Community in the frame work of the project Catalysis by Metal Complexes involving Small Molecules(ERBCHRXCT930147).

Peer reviewed