Dinuclear Ruthenium Ethylene Complexes: Syntheses, Structures, and Catalytic Applications in ATRA and ATRC Reactions

Abstract

The complexes [( p -cymene)Ru(μ-Cl) 3 RuCl(C 2 H 4 )(PR 3 )] (PR 3 = PPh 3, P n -Bu 3 ) were synthesized by reaction of [( p -cymene)RuCl(μ-Cl)] 2 with the respective phosphine ligand in the presence of ethylene. Structurally related complexes containing the tricyclopentylphosphine (PCyp 3 ) or the isobutylphobane ligand (phobane = 9-phosphabicyclo[3.3.1]nonane) were obtained by reaction of [(arene)RuCl(μ-Cl)] 2 (arene = p -cymene, 1,3,5- i -Pr 3 C 6 H 3 ) with 2 equiv of [(arene)RuCl 2 (PCyp 3 )] or [(arene)RuCl 2 (isobutylphobane)] in the presence of ethylene. The structures of the dinuclear complexes [( p -cymene)Ru(μ-Cl) 3 RuCl(C 2 H 4 )(PPh 3 )] and [(1,3,5- i -Pr 3 C 6 H 3 )Ru(μ-Cl) 3 RuCl(C 2 H 4 )(isobutylphobane)] as well as of the mononuclear precursors [( p -cymene)RuCl 2 (isobutylphobane)], [(1,3,5- i -Pr 3 C 6 H 3 )RuCl 2 (isobutylphobane)], and [( p -cymene)RuCl 2 (PCyp 3 )] were determined by single-crystal X-ray analyses. Kinetic analyses of the atom transfer radical addition reaction of CCl 4 to styrene revealed that the catalytic activity of the dinuclear complexes was strongly dependent on the nature of the phosphine ligand but only slightly affected by the nature of the arene ligand. Addition of Mg to the reaction mixture was found to increase the lifetime of the catalyst significantly. With Mg as the cocatalyst, mixed-valence Ru(II)−Ru(III) complexes of the general formula [(arene)Ru(μ-Cl) 3 RuCl 2 (PR 3 )] were found to be equally potent catalyst precursors when compared to the Ru(II)−Ru(II) complexes [(arene)Ru(μ-Cl) 3 RuCl(C 2 H 4 )(PR 3 )].