Half sandwich ruthenium(ii) hydrides: hydrogenation of terminal, internal, cyclic and functionalized olefins

Abstract

Bis(1,2,3-triazolylidene) silver(I) complex 1a was reacted with [RuCl₂(p-cymene)]₂ to give the ruthenium complex [PhCH₂N₂(NMe)C₂(C₆H₄CF₃)]RuCl₂(p-cymene) (2a) as major product in addition to the minor C(sp²)–H activated product [PhCH₂N₂(NMe)C₂(C₆H₃CF₃)]RuCl(p-cymene) (2a′). Similar ruthenium complexes 2b, 2c, 2d and 2e with general formula RuCl₂(p-cymene)(NHC) (NHC = MesCH₂N₂(NMe)C₂Ph 2b, PhCH₂N₂(NMe)C₂Ph 2c, TripCH₂N₂(NMe)C₂Ph 2d, IMes 2e) were also synthesized. Subsequent reaction of Me₃SiOSO₂CF₃ with 2a and 2b resulted in cationic ruthenium species [(PhCH₂N₂(NMe)C₂(C₆H₄CF₃))RuCl(p-cymene)][OSO₂CF₃] (3a) and [(MesCH₂N₂(NMe)C₂Ph)RuCl(p-cymene)][OSO₂CF₃] (3b), respectively. Complexes 3a and 3b dissolved in CD₃CN to give [(PhCH₂N₂(NMe)C₂(C₆H₄CF₃))RuCl(CD₃CN)(p-cymene)][OSO₂CF₃] (4a) and [(MesCH₂N₂(NMe)C₂Ph)RuCl(CD₃CN)(p-cymene)][OSO₂CF₃] (4b), respectively. Cationic ruthenium species 4a and 4b failed to show catalytic activity towards hydrogenation of olefins. Ruthenium(II) complexes 2b–e with the general formula RuCl₂(p-cymene)(NHC) were reacted with Et₃SiH to generate a series of ruthenium(II) hydrides 5b–e. These compounds 5b–e are effective catalysts for the hydrogenation of terminal, internal and cyclic and functionalized olefins.