Carbamato-benzylidene ruthenium chelates – Synthesis, structure and catalytic activity in olefin metathesis

Abstract

New carbamato-κN-benzylidene ruthenium chelates were synthesized from the first [RuCl2(PCy3)2(=CHPh)] and second [RuCl2(SIMes)(PCy3)(=CHPh)] generation Grubbs catalysts by metathetic exchange of benzylidene ligand for tert-butyl (2-vinylphenyl)carbamates bearing benzylidene ligand substituted in the position para to carbamato functionality with methyl or trifluoromethyl group. In all metathetical transformations tested, i.e. in ROMP of cycloocta-1,5-diene, RCM of diethyl diallylmalonate and diethyl 2-allyl-2-(2-methylallyl)malonate and cross-metathesis of allylbenzene with Z-1,4-diacetoxybut-2-ene, the complexes behave like latent catalysts. Complexes remain completely inactive until they are activated by the addition of ethereal solution of HCl. The presence of the electron-withdrawing group results in a slight increase in the catalytic activity of the activated form of the catalyst relative to a similar form of the unsubstituted complex or the least active complex carrying the electron donating group.