Reaction of Ru(1−6-η-cyclooctatriene)(η2-dimethyl fumarate)2 with Monodentate and Bidentate Phosphines: A Model Reaction of Catalytic Dimerization of Alkenes

Abstract

Ru(1−6-η-cyclooctatriene)(η2-dimethyl fumarate)2 1 reacts with monodentate tertiary phosphine ligands, PPh3, PMePh2, PMe2Ph, and PEt3, to give novel ruthenium(0) phosphine complexes, Ru(1−6-η-cyclooctatriene)(η2-dimethyl fumarate)(L) [L = PPh3 (2a), PMePh2 (2b), PMe2Ph (2c), and PEt3 (2d)], in high yields. The structures of the complexes 2b, 2c, and 2d were determined by X-ray analyses. The coordination geometry of the complexes around the central ruthenium atom is a highly distorted trigonal bipyramid, but the orientation of coordination of the cyclooctatriene ligand differs from each other. Complexes 2a−d show dynamic behavior in solution involving 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(η2-dimethyl fumarate)(dppe)2 4 and 5 [dppe = 1,2-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 the central ruthenium atom is a trigonal bipyramid and that of 5 is octahedral. Complex 5 is generated through the activation of the sp2 carbon−hydrogen bond of dimethyl fumarate and then the insertion of the other dimethyl fumarate into the formed ruthenium−hydrogen bond, followed by the coordination of the two carbonyl groups of the esters. The treatment of 5 with 1 atm of carbon monoxide afforded 6, the structure of which was confirmed by X-ray analysis. Complex 5 reacted with 60 atm of carbon monoxide to give dimers of dimethyl fumarate and Ru(CO)3(dppe) via reductive elimination.