1,2,3-Triazolylidene ruthenium(ii)-cyclometalated complexes and olefin selective hydrogenation catalysis

Abstract

Silver(I) 1,2,3-triazol-5-ylidenes [(RCH₂C₂N₂(NMe)Ph)₂Ag][AgCl₂] (R = Ph 3a, C₆H₂iPr₃3b, C₆H₂Me₃3c) and [(PhCH₂C₂N₂(NMe)R)₂Ag][AgCl₂] (R = C₆H₄Me 3d, C₆H₄CF₃3e) were synthesized and subsequently treated with RuHCl(PPh₃)₃ and RuHCl(H₂)(PCy₃)₂. The reaction of 3a with RuHCl(PPh₃)₃ gave RuHCl(PPh₃)₂(PhCH₂C₂N₂(NMe)Ph) (4a₁) as the minor product and the cyclometalated complex RuCl(PPh₃)₂(PhCH₂C₂N₂(NMe)C₆H₄) (4a₂) as the major product. However, similar reaction with 3b selectively formed the cyclometalated complex RuCl(PPh₃)₂((C₆H₂iPr₃)CH₂C₂N₂(NMe)C₆H₄) (4b₂). Similarly the silver(I) triazolylidenes 3a and 3b were reacted with RuHCl(H₂)(PCy₃)₂; gave RuHCl(PCy₃)₂(PhCH₂C₂N₂(NMe)Ph) (5a₁), RuCl(PCy₃)₂(PhCH₂C₂N₂(NMe)C₆H₄) (5a₂) and RuCl(PCy₃)₂((C₆H₂iPr₃)CH₂C₂N₂(NMe)C₆H₄) (5b₂), respectively. Species 3c, 3d and 3e resulted in the cyclometalated complexes (5c₂, 5d₂ and 5e₂) as the major products as well as the ruthenium-hydride complexes (5c₁, 5d₁ and 5e₁) as the minor products. The cyclometalated species are derived from the ruthenium-hydride complexes via C(sp²)–H activation. These Ru-complexes were shown to act as hydrogenation catalyst precursors for olefinic substrates including those containing a variety of functional groups.