Supported organometallic complexes. XXXVIII - Bis(methoxyethyldimethylphosphine)ruthenium(II) complexes as transfer hydrogenation catalysts

Diamineruthenium(II) complexes containing the hemilabile methoxyethyldimethylphosphine ligand, [Cl2Ru(L-n)(eta(1)-Me2PCH2CH2OMe)(2)] (2L(n)) (n = 1-12, Scheme 1), have been synthesized from the starting materials Me2PCH2CH2OMe, [Ru(COD)Cl-2](n), and the respective diarnines L-1-L-12. The structure of complex 2L(5) reveals that two chlorides are in trans position, while in complex 2L(11) the two chlorides favor a cis configuration. Most of the complexes are highly catalytic active in the hydrogen transfer reduction of acetophenone. The experimental study indicates that the replacement of phenyl groups for methyl functions in the ether-phosphine ruthenium(II) complexes resulted in a switch of the hydrogenation mechanism from direct hydrogenation to transfer hydrogenation. The reason is attributed to the better donor ability of methyl groups compared to phenyl substitutents. Thus the metal center becomes more electron-rich and inhibits the binding of dihydrogen to the ruthenium(II) complex fragment.