Reaction of Ru(1-6-eta-cyclooctatriene)(eta(2)-dimethyl fumarate)(2) with monodentate and bidentate phosphines: A model reaction of catalytic dimerization of alkenes

Ru(1-6-eta -cyclooctatriene)(eta (2)-dimethyl fumarate)(2) 1 reacts with mo nodentate tertiary phosphine ligands, PPh3, PMePh2, PMe2Ph, and PEt3, to gi ve novel ruthenium(0) phosphine complexes, Ru(1-6-eta -cyclooctatriene)(eta (2)-dimethyl fumarate)(L) [L = PPh3 (2a), PMePh2 (2b), PMe2Ph (2c), and PE t3 (2d)], in high yields. The structures of the complexes 2b, 2c; and 2d we re determined by X-ray analyses. The coordination geometry of the complexes around the central ruthenium atom is a highly distorted. trigonal bipyrami d, but the orientation of coordination of the cyclooctatriene ligand differ s from. each other. Complexes 2a-d show dynamic behavior in solution involv ing the rotation of the cyclooctatriene ligand around the axis, which lies between the ruthenium center and the center of the cyclooctatriene ligand. Novel bidentate phosphine complexes, Ru(eta (2)-dimethyl fumarate)(dppe)(2) 4 and Ru[C(CO2CH3)=CHC(O)OCH3][CH(CO2CH3)CH2C(O)OCH3](dppe) 5 [dppe = 1,3- bis-(diphenylphosphino)ethane] were prepared by the reaction of 1 with dppe in high yields. The structures of the complexes 4 and 5 were determined by single-crystal X-ray diffraction. The coordination geometry of 4 around th e central ruthenium atom is a trigonal bipyramid and that of 5 is octahedra l. Complex 5 is generated through the activation of the sp(2) carbon-hydrog en bond of dimethyl fumarate and then the insertion of the other dimethyl f umarate into the formed ruthenium-hydrogen bond, followed by the coordinati on of the two carbonyl groups of the esters. The treatment of 5 with 1 atm of carbon monoxide afforded Ru[C(CO2CH3)=CHC(O)OCH3][CH(CO2CH3)CH2C(O)OCH3] (CO)(dppe) 6, the structure of which was confirmed by X-ray analysis. Compl ex 5 reacted with 60 atm of carbon monoxide to give dimers of dimethyl fuma rate and Ru(CO)3(dppe) via reductive elimination.