Allenylidene to Indenylidene Rearrangement in Arene-Ruthenium Complexes : a Key Step to Highly Active Catalysts for Olefin Metathesis Reactions

Autores: Ricardo Castarlenas, Chloé Vovard, Cédric Fischmeister, Pierre H. Dixneuf Ref. revista: Journal of the American Chemiscal Society, 128, 4079-4089, (2006)

The allenylidene-ruthenium complexes [(è6-arene)RuCl(dCdCdCR2)(PR¢3)]OTf (R2 ) Ph; fluorene, Ph, Me; PR¢3 ) PCy3, PiPr3, PPh3) (OTf ) CF3SO3) on protonation with HOTf at -40 °C are completely transformed into alkenylcarbyne complexes [(è6-p-cymene)RuCl(tCCHdCR2)(PR3)](OTf)2. At -20 °C the latter undergo intramolecular rearrangement of the allenylidene ligand, with release of HOTf, into the indenylidene group in derivatives [(è6-arene)RuCl(indenylidene)(PR3)]OTf. The in situ-prepared indenylidene-ruthenium complexes are efficient catalyst precursors for ring-opening metathesis polymerization
of cyclooctene and cyclopentene, reaching turnover frequencies of nearly 300 s-1 at room temperature. Isolation of these derivatives improves catalytic activity for the ring-closing metathesis of a variety of dienes and enynes. A mechanism based on the initial release of arene ligand and the in situ generation of the active catalytic species RuCl(OTf)(dCH2)(PR3) is proposed.