Versatile Ru-based metathesis catalysts designed for both homogeneous and heterogeneous processes

Abstract

The synthesis of new ruthenium-based catalysts applicable for both homogeneous and heterogeneous metathesis is described. Starting from the Hoveyda-Grubbs first generation ( 1) and the Hoveyda-Grubbs second generation ( 2) catalysts the homogeneous catalysts [RuCl((RO) 3Si–C 3H 6–N(R′)–CO–C 3F 6–COO)( CH– o-O– iPr–C 6H 4)(SIMes)] ( 4: R = Et, R′ = H; 5: R = R′ = Me) (SIMes = 1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene) were prepared by substitution of one chloride ligand with trialkoxysilyl functionalized silver carboxylates (RO) 3Si–C 3H 6–N(R′)–CO–C 3F 6–COOAg ( 3a: R = Et, R′ = H; 3b: R = R′ = Me). These homogeneous ruthenium-species are among a few known examples with mixed anionic ligands. Exchange of both chloride ligands afforded the catalysts [Ru((RO) 3Si–C 3H 6–N(R′)–CO–C 3F 6–COO)( CH– o-O– iPr–C 6H 4)(SIMes)] ( 9: R = Et, R′ = H; 11: R = R′ = Me) and [Ru((RO) 3Si–C 3H 6–N(R′)–CO–C 3F 6–COO)( CH– o-O– iPr–C 6H 4)(PCy 3)] ( 8: R = Et, R′ = H; 10: R = R′ = Me). The reactivity of the new complexes was tested in homogeneous ring-closing metathesis (RCM) of N, N-diallyl- p-toluenesulfonamide and TONs of up to 5000 were achieved. Heterogeneous catalysts were obtained by reaction of 4, 5 and 8– 11 with silica gel (SG-60). The resultant supported catalysts 4a, 5a, 8a– 11a showed reduced activity compared to their homogenous analogues, but rival the activity of similar heterogeneous systems.