Ruthenium carbene complexes bearing an anionic carboxylate chelated to a hemilabile ligand

A series of bidentate ruthenium-based NHC complexes with the general formula [(H(2)IMes)(kappa(2)-L-COO)ClRu=CHPh)], where L is either PAr(3), HNR(2), or ROR, were prepared from commercially available [(H(2)IMes)(PCy(3))Cl(2)Ru(CHPh)] (2) and the appropriate ligand. The catalytic activities of the complexes were evaluated in ring-closing metathesis reactions. The type of donor ligand has a major impact on both the initiation behavior and also the stability of the complexes. Upon addition of CuCl to the reaction mixture the initiation is improved for the phosphine or amine containing chelates. For the P,O-chelate, the fast initiation was followed by decomposition. In the case of the N,O-containing chelate, a stable catalytic system was achieved. Trapping experiments support that the nitrogen lone-pair reversibly coordinates CuCl during the reaction.