Synthesis and reactivity of neutral and cationic ruthenium(II) tris(pyrazolyl)borate alkylidenes

A series of neutral and cationic ruthenium(II) alkylidenes containing the h ydrotris(pyrazolyl)borate (Tp) ligand have been prepared. The complex Tp(PC y3)(Cl)Ru=CHPh (2) was obtained by the reaction of (PCy3)(2)(Cl)(2)Ru=CHPh (1) and KTp. Treatment of 2 with AgBF4 or AgSbF6 in the presence of a varie ty of coordinating solvents afforded [Tp(PCy3)(L)Ru=CHPh](+) (L = H2O, CH3C N, pyridine) in high yield. The dynamic NMR behavior of these new complexes is discussed, and the X-ray crystal structure of [Tp(PCy3)(H2O)Ru=CHPh]BF4 (3) is reported. Alkylidenes 2-5 alone do not catalyze olefin metathesis r eactions. However, complex 2 is activated for ring-closing metathesis by th e addition of HCl, CuCl, and AlCl3.