Syntheses and Structures of Ruthenium(II) N,S-Heterocyclic Carbene Diphosphine Complexes and their Catalytic Activity towards Transfer Hydrogenation

摘要

Phosphine exchange of [Ru~(II)Br(MeCOO)(PPh_(3))_(2)(3-RBzTh)] (3-RBzTh velence 3-benzylbenzothiazol-2-ylidene) with a series of diphosphines (bis(diphenylphosphino)methane (dppm), 1,2-bis(diphenylphosphino)-ethylene (dppv), 1,1'-bis(diphenylphosphino)ferrocene (dppf), 1,4-bis(diphenylphosphino)butane (dppb), and 1,3-(diphenylphosphino)propane (dppp)) gave mononuclear and neutral octahedral complexes [RuBr(MeCOO)((eta)~(2)-P_(2))(3-RBzTh)] (P_(2) velence dppm (2), dppv (3), dppf (4), dppb (5), or dppp (6)), the coordination spheres of which contained four different ligands, namely, a chelating diphosphine, carboxylate, N,S-heterocyclic carbene (NSHC), and a bromide. Two geometric isomers of 6 (6a and 6b) have been isolated. The structures of these products, which have been elucidated by single-crystal X-ray crystallography, show two structural types, I and II, depending on the relative dispositions of the ligands. Type I structures contain a carbenic carbon atom trans to the oxygen atom, whereas two phosphorus atoms are trans to bromine and oxygen atoms. The type II system comprises a carbene carbon atom trans to one of the phosphorus atoms, whereas the other phosphorus is trans to the oxygen atom, with the bromine trans to the remaining oxygen atom. Complexes 2, 3, 4, and 6a belong to type I, whereas 5 and 6b are of type II. The kinetic product 6b eventually converts into 6a upon standing. These complexes are active towards catalytic reduction of paramethyl acetophenone by 2-propanol at 82 deg C under 1percent catalyst load giving the corresponding alcohols. The dppm complex 2 shows the good yields (91-97percent) towards selected ketones.