2018 Volume 76 Issue 12 Pages 1301-1309
Design and synthesis of supporting ligands for transition-metal complexes are significant as an efficient method for development of new metal complex catalysts for organic synthesis. Metal complexes bearing chelate-type silyl supporting ligands are expected to show high catalytic performance toward activation of inert bonds such as C-H due to the strongly σ-donating and trans-labilizing properties of their silyl ligand moieties. This article describes recent progress of synthesis and catalysis of transition-metal complexes bearing a xanthene-based bis(silyl)supporting ligand “xantsil”, developed by our previous study, and a related silyl(phosphine)-xanthene chelate ligand “xantSiP”. These complexes were synthesized straightforwardly by reactions of (hydrosilyl)xanthene derivatives as ligand precursors with low-valent metal complexes via Si-H activation and ligand substitution. As a prominent result, the reaction of arylalkynes with hydrosilanes catalyzed by 16-electron ruthenium-xantsil complexes with bulky trialkylphosphine was found to give 2-silylstyrenes via ortho-C-H silylation and trans-selective hydrogenation (ortho-C-H silylation/hydrogenation). On the other hand, when catalysts with triaminophosphine instead of trialkylphosphine were used for the reaction, 2,α-bis(silyl)styrenes were formed in most cases via ortho-C-H silylation and trans-selective hydrosilylation (ortho-C-H silylation/hydrosilylation). These novel C-H silylation reactions proceeded under mild conditions(room temp.∼70 °C).
