Decomposition of Ruthenium Olefin Metathesis Catalysts.
The decompn. of a series of ruthenium metathesis catalysts was examd. using phosphine and imidazolidinylidene methylene species [(L1)(L2)X2Ru:CH2] (L1, L2 = PCy3, 1,3-Ar2C3H4N2-κC2; Ar = mesityl, 2,6-iPrC6H3) as model complexes. All of the phosphine-contg. methylene complexes decompd. to generate methylphosphonium salts, and their decompn. routes followed first-order kinetics. The formation of these salts in high conversion, coupled with the obsd. kinetic behavior for this reaction, suggests that the major decompn. pathway involves nucleophilic attack of a dissocd. phosphine on the methylene carbon. This mechanism also is consistent with decompn. obsd. in the presence of ethylene as a model olefin substrate. The decompn. of phosphine-free catalyst (H2IMes)(Cl)2Ru:CH(2-C6H4-O-i-Pr) (H2IMes = 1,3-dimesityl-imidazolidin-2-ylidene) with ethylene was found to generate unidentified ruthenium hydride species. The novel ruthenium complex (H2IMes)( py)3(Cl)2Ru, which was generated during the synthetic attempts to prep. the highly unstable pyridine-based methylidene complex [(H2IMes)(Py)2(Cl)2Ru:CH2], is also reported. [on SciFinder(R)]