Synthesis and characterization of mono- and tri-nuclear ruthenium complexes of 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl and their catalytic activity

Abstract

The Structures of ruthenium(II) complexes formed in solution from [RuX{(S)-binap}(arene)]Y (S)-3(X, Y = halide and/or BF₄ ^–; binap = 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl; arene = benzene or p-cymene) depend on the solvent. In acetonitrile–methanol (1 : 1) dicationic complexes [Ru{(S)-binap}(MeCN)₄]X(Y)(S)-4(X = Y = Cl a; X = Cl, Y = BF₄b; X = Y = Br c; or X = Y = I d) are predominantly formed, while monocationic species [RuX{(S)-binap}(MeCN)₃]X (S)-6(X = Cl a, Br b or I c) were observed in acetonitrile. These mono- and di-cationic species could not be isolated pure, while [RuCl₂{(S)-binap}(MeCN)₂](S)-5 was isolated from (S)-4a or (S)-6a upon concentration of the reaction mixture. In methanol without donor molecules such as acetonitrile, cationic trinuclear complexes [Ru₃X₅{(S)-binap}₃]Y (S)-7(X = Y = Cl a; X = Cl, Y = BF₄b or X = Y = Br c) were exclusively formed by heating at 60 °C or UV irradiation of a solution of (S)-3. The structure of (S)-7 was characterized by spectral data and an X-ray crystallographic analysis of (S)-7b[orthorhombic, space group P2₁2₁2₁, a= 26.328(5), b= 18.140(3), c= 26.374(4), Z= 4, R′= 0.083]. The relationship between the structure of the Ru^II(binap) complexes and their catalytic activities for asymmetric hydrogenation of methyl 3-oxobutanoate has been investigated.