The new hydridoruthenium complexes RuH-Cl(CO)(NHC)(PPh 3 ) (NHC ) IMes (4a), H 2 IMes (4b)), conveniently accessible from RuHCl(CO)(PPh 3 ) 3 , exhibit high activity for hydrogenation of unactivated internal olefins and isomerization of terminal olefins. The lability of the PPh 3 ligand is fundamental to the utility of 4: where this group is replaced by the relatively nonlabile PCy 3 ligand, the activating effect of the N-heterocyclic carbene is suppressed.N-Heterocyclic carbenes (NHCs) have emerged as an exceptionally versatile class of ligands for transitionmetal catalysis. Owing to their enhanced σ-donating ability and thermal stability, 1,2 NHC derivatives display higher reactivity than the corresponding phosphine complexes in many Ru-catalyzed olefin metathesis reactions 3-7 and Pd-catalyzed coupling reactions. 8 They can also offer advantages over the thermally sensitive Crabtree catalyst in the Ir-catalyzed H 2 -hydrogenation of olefins. 9,10 While good to excellent activity, typically at high catalyst loadings, has been reported in transfer hydrogenation (or in some cases, direct hydrogenation) via NHC complexes of rhodium, 11 iridium, 9-11 nickel, 12
Clean, high-yield routes are established to the important catalyst chlorobis(tricyclohexyl- , or with the appropriate NHC ligand, then PCy 3 . Advantages over prior routes to these complexes lie in the high yields from a conveniently accessible precursor, the absence of by-products that otherwise prove difficult to remove, and the short reaction times under experimentally convenient conditions.
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