Four tetranuclear ruthenium carbonyl hydrido clusters consisting of the enantiomeric pairs [H 4 Ru 4 (CO) 10 {µ-1,2-(R/S,R/S)-bdpp}] and [H 4 Ru 4 (CO) 10 {1,1-(R/S,R/S)-bdpp}] containing chiral (R,R)-or (S,S)-bdpp [bdpp ) (2R/S,4R/S)-2,4-bis(diphenylphosphino)pentane] have been prepared and fully characterized. These clusters catalyze asymmetric hydrogenation of tiglic acid [trans-2-methyl-2-butenoic acid] with high conversion rates (75-100%) under relatively mild reaction conditions. Enantiomeric excesses of 40-46% were observed; the predominating enantiomeric form of the hydrogenated product is dependent on the configuration of the diphosphine ligand, indicating strong chiral induction.

Ru(II) bipyridine complexes were synthesized and their spectroscopic properties studied. The replacement of 2,2‘-bipyridine (bpy) by 6,6‘-dimethyl-substituted 2,2‘-bipyridine (dmbpy) is suggested to change the steric and electronic factors involved in these complexes, which in turn affect the coordination ability of Ru. In the case of thiocyanate ligand, the metal center is able to coordinate to either its S or N end, the bonding mode being dependent on both steric and electronic factors.

The chiral clusters [H(4)Ru(4)(CO)(12-n)(L)(n)] (n = 1, 2; L = NMDPP), 1,1-[H(4)Ru(4)(CO)(10)(L-L)] (L-L = DUPHOS, DIPAMP), 1,2-[H(4)Ru(4)(CO)(10)(DIOP)] and [{H(4)Ru(4)(CO)(10)(DIOP)}(2)] have been synthesized by derivatizing the parent carbonyl cluster [H(4)Ru(4)(CO)(12)] with the appropriate mono- or didentate chiral phosphine ligand. The phosphine-substituted clusters were found to be able to catalyze the (asymmetric) hydrogenation of tiglic acid albeit with relatively low selectivity (enantiomeric excesses varying from 0 to 23%). It was found that the stability of the chiral ruthenium hydride clusters and the product distribution obtained in the catalytic reactions are dependent on the nature of the chiral phosphine. The crystal structures of [H(4)Ru(4)(CO)(12-n)(L)(n)] (n = 1, 2; L = NMDPP), 1,1-[H(4)Ru(4)(CO)(10)(L-L)] (L-L = DUPHOS, O-DUPHOS (partially oxygenated ligand), DIPAMP), 1,2-[H(4)Ru(4)(CO)(10)(DIOP)] and [{H(4)Ru(4)(CO)(10)(DIOP)}(2)] are presented.