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)_2Ru=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_2O, CH_3CN, 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_2O)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.

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