Radical anion forming activity of the Grubbs' catalyst and related organometallics: Michael accepters as metathesis promoters

When several p-benzoquinones in methylene chloride solution are mixed at ro om temperature with RuCl2(PCy3)(2)(CHPh), RuCl2(PPh3)(3), RhCl(PPh3)(3) and CoBr2(PPh3)(2), strong, well-resolved, persistent epr signals are observed , consistent with the formation of radical anions. In the case of the Grubb s' catalyst, RuCl2(PCy3)(2)(CHPh), evidence is presented that these signals arise from charge transfer. The Grubbs' catalyst, is also remarkable in th at similar epr activity is observed using norbsmadienes, and to a lesser ex tent during and after metathesis polymerisation of norbornene and cyclopent ene. The dienes are also much more efficient promoters of initiation of the se polymerisations than the monoenes, and evidence is presented that the pr esence of p-benzoquinone enhances the reactivity of the propagating metalla carbenes. (C) 2000 Elsevier Science S.A. All rights reserved.