Six-coordinate alkynyldiphenylphosphine ruthenium(II) complexes: Synthesis, structure, and catalytic activity as ROMP initiators

Six-coordinate [trans-RuCl2(PPh2C equivalent to CR)(4)] (R = Ph (1), (4-CH3)C6H4 (2), (4-OCH3)C6H4, (3), (4CF(3))C6H4 (4)) were obtained from the reaction of RuCl3 center dot xH(2)O with the appropriate alkynylphosphine (PPh2C equivalent to CR) in ethanol. An X-ray crystal structure analysis of 1 center dot 4H(2)O 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 center dot center dot center dot pi(C equivalent to 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 equivalent to 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.