Synthesis and Reactivity of Neutral and Cationic Ruthenium(II) Tris(pyrazolyl)borate Alkylidenes

Abstract

A series of neutral and cationic ruthenium(II) alkylidenes containing the hydrotris(pyrazolyl)borate (Tp) ligand have been prepared. The complex Tp(PCy 3 )(Cl)Ru CHPh ( 2 ) was obtained by the reaction of (PCy 3 ) 2 (Cl) 2 Ru CHPh ( 1 ) and KTp. Treatment of 2 with AgBF 4 or AgSbF 6 in the presence of a variety of coordinating solvents afforded [Tp(PCy 3 )(L)Ru CHPh] + (L = H 2 O, CH 3 CN, pyridine) in high yield. The dynamic NMR behavior of these new complexes is discussed, and the X-ray crystal structure of [Tp(PCy 3 )(H 2 O)Ru CHPh]BF 4 ( 3 ) is reported. Alkylidenes 2 − 5 alone do not catalyze olefin metathesis reactions. However, complex 2 is activated for ring-closing metathesis by the addition of HCl, CuCl, and AlCl 3 .