Six-Coordinate Alkynyldiphenylphosphine Ruthenium(II) Complexes:  Synthesis, Structure, and Catalytic Activity as ROMP Initiators

Six-coordinate [trans-RuCl2(PPh2C⋮CR)4] (R = Ph (1), (4-CH3)C6H4 (2), (4-OCH3)C6H4, (3), (4-CF3)C6H4 (4)) were obtained from the reaction of RuCl3·xH2O with the appropriate alkynylphosphine (PPh2C⋮CR) in ethanol. An X-ray crystal structure analysis of 1·4H2O reveals that the complex is obtained as the trans isomer, with the halides occupying apical positions and the phosphorus atoms lying in the equatorial plane. The alkynyl substituents of adjacent P ligands are alternatively pointing up and down and are maintained within the vertical plane by a set of weak hydrogen interactions [intra C−H···Cl and C−H···π(C⋮CPh)] connecting the ortho-H of the phenyl rings with the chloride and acetylenic moieties, respectively. Complexes 1 and 2 react cleanly with phenylacetylene via dissociative loss of one alkynyphosphine ligand to yield saturated 18 e- Ru(II) vinylidene complexes [mer,cis-RuCl2(CCHPh)(PPh2C⋮CR)3] (R = Ph (12), Tol (13)). The catalytic activity of 1−4 in ROMP reactions of norbornene and several functionalized norbornenes in the presence of trimethylsilyldiazomethane (TMSD) as the carbene source is also described.