An-Najah Staff

Diamineruthenium(II) complexes containing the hemilabile methoxyethyldimethylphosphine ligand, [Cl2Ru(Ln)(η1-Me2PCH2CH2OMe)2] (2Ln) (n = 1-12, Scheme 1), have been synthesized from the starting materials Me2PCH2CH2OMe, [Ru(COD)Cl2]n, and the respective diamines L1-L12. The structure of complex 2L5 reveals that two chlorides are in trans position, while in complex 2L11 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.

The novel trans-[Cl2Ru(II)(PPh3)2(3,4-diaminophenyl)(phenyl)methanone] complex was obtained by reacting RuCl2(PPh3)3 with equimolar amounts of (3,4-diaminophenyl)(phenyl)methanone as diamine co-ligand in CH2Cl2. One of the PPh3 ligand was quantitatively exchanged by (3,4-diaminophenyl)(phenyl)methanone, even when excess diamine was added. The trans-RuCl2 desired complex was characterized on the basis of elemental analysis, elemental analysis, FAB-MS, IR, UV-vis, 1H, 13C and 31P{1H}NMR.

The novel diamine(dppp)ruthenium(II) complexes 3L1–3L12 have been obtained by reaction of equimolar amounts of Cl2Ru(dppp)2 (2) with the diamines L1–L12 in excellent yields. Within a few minutes one of the diphosphine ligands was quantitatively exchanged by the corresponding diamine. X-ray structural investigations of 3L1, 3L2, and 3L8 show triclinic unit cells with the space groups PView the MathML source (3L1, 3L2) and P 1 (3L8). Whereas in solution all these complexes prefer a trans-RuCl2 configuration, in the solid state cis-(3L1, 3L2) and trans-isomers (3L8) were observed. With the exception of 3L5, 3L6, and 3L12 all mentioned ruthenium complexes are highly catalytically active in the hydrogenation of the α,β-unsaturated ketone trans-4-phenyl-3-butene-2-one. In most cases the conversions and selectivities toward the formation of the unsaturated alcohol trans-4-phenyl-3-butene-2-ol were >99% with high turnover frequencies (TOFs) under mild conditions.