Asymmetric hydrogenation of an α-unsaturated carboxylic acid catalyzed by intact chiral transition metal carbonyl clusters-diastereomeric control of enantioselectivity

Twenty clusters of the general formula [(μ-H)₂Ru₃(μ₃-S)(CO)₇(μ-P-P∗)] (P-P∗ = chiral diphosphine of the ferrocene-based Walphos or Josiphos families) have been synthesised and characterised. The clusters have been tested as catalysts for asymmetric hydrogenation of tiglic acid [trans-2-methyl-2-butenoic acid]. The observed enantioselectivities and conversion rates strongly support catalysis by intact Ru₃ clusters. A catalytic mechanism involving an active Ru₃ catalyst generated by CO loss from [(μ-H)₂Ru₃(μ₃-S)(CO)₇(μ-P-P∗)] has been investigated by DFT calculations.