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

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–C3H6–N(R′)–CO–C3F6–COO)(CH–o-O–iPr–C6H4)(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–C3H6–N(R′)–CO–C3F6–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–C3H6–N(R′)–CO–C3F6–COO)(CH–o-O–iPr–C6H4)(SIMes)] (9: R = Et, R′ = H; 11: R = R′ = Me) and [Ru((RO)3Si–C3H6–N(R′)–CO–C3F6–COO)(CH–o-O–iPr–C6H4)(PCy3)] (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.

The selective exchange of one or both chloride ligands in the Hoveyda-Grubbs first and second generation catalysts with partially fluorinated trialkoxysilyl-containing silver(I) carboxylates has been achieved. This gives access to ruthenium catalysts which can be used both homogeneously or immobilized on silica. The synthesis and reactivity of these complexes are described including the monocarboxylate ruthenium catalysts [RuCl((RO)3Si–C3H6–N(R′)–CO–C3F6–COO)(CH–o-O–iPr–C6H4)(SIMes)] (R = Et, R′ = H and R = R′ = Me).Figure optionsDownload as PowerPoint slide