Trimerisation of the cationic fragments [(eta-ring)M(Aa)](+) ((eta-ring) M= (eta(5)-C5Me5)Rh, (eta(5)-C5Me5)Ir, (eta(6)-p-MeC(6)H(4)iPr)Ru; Aa = alpha-amino acidate) with chiral self-recognition: Synthesis, characterization, solution studies and catalytic reactions of the trimers [{(eta-ring)M(Aa)}(3)](BF4)(3)

The mononuclear neutral chlorides [(eta-ring)M(Aa)Cl] ((eta-ring)M=(eta(5)- C5Me5)Rh, (eta(5)-C5Me5)Ir, (eta(6)-pMeC(6)H(4)iPr)Ru; Aa = alpha-amino aci date) were treated with AgBF4 to yield the corresponding new chiral trimers [{(eta-ring)M(Aa)}(3)](BF4)(3). Compounds [{(eta(5)-C5Me5)Ir(Ala)}(3)] (BF 4)(3) (Ib) and [{(eta(6)-pMeC(6)H(4)iPr)Ru(L-Pro)}(3)] (BF4)(3) (6c) were c haracterised by X-ray diffraction. Trimerisation takes place by chiral self -recognition: the trimers RMRMRM (rho isomer) or SMSMSM (sigma isomer), whi ch have equal configuration at the metal centre, were the only diastereomer s detected. In solution, a diastereomerisation process between both isomers occurs, where the equilibrium constant depends on the solvent, amino acida te, and metal. The different localisation of the polar groups (NH or NH, mo ieties) on the molecular surface of the two diastereomers (rho and sigma) p rovides a qualitative explanation for the different diastereomer stability observed in solution. The new chiral trimers catalyse the reduction of unsa turated aldehydes to unsaturated alcohols by hydrogen transfer from aqueous sodium formate and the reduction of acetophenone by hydrogen transfer from 2-propanol with up to 75 % ee.