New ruthenium benzylidene complexes (3) bearing N-heterocyclic carbene and chelating phosphino-carboxylate ligands were easily prepared by the reaction of (H2IMe)(PPh3)(Cl)(2)Ru=CHPh (1) [H2IMe=1,3-bis(2,6-dimethylphenyl)-4,5-dihydroimidazol-2-ylidene] with corresponding phosphino-carboxylates 2. Catalysts featuring a five-membered or rigid six-membered chelating ring proved to exhibit enhanced stability and high catalytic efficiency toward the ring-closing metathesis (RCM) reaction of diethyl diallylmalonate and diallylmalononitrile. (c) 2007 Elsevier B.V. All rights reserved.