Indenylidene-ruthenium complexes bearing saturated N-heterocyclic carbenes: Synthesis and catalytic investigation in olefin metathesis reactions

The synthesis of complexes of the general formula Cl2Ru-(SIMes)(L)(3-phenylinden-1-ylidene) (5, L = PCy3; 6, L = py; and 7, L = PPh3) from Cl2Ru(PR3)(2)(3-phenylinden-1-ylidene) (2a, R = Ph; 2b, R = Cy) is reported. This family of olefin metathesis catalysts was fully characterized (H-1, C-13 and P-31 NMR spectroscopy and elemental analysis) and provided excellent activity in the ring-opening metathesis polymerization of 1,5-cyclooctadiene and the ring-closing metathesis of diethyl diallylmalonate. Comparison with the corresponding benzylidene-containing catalysts, 1a,c and 8b, established the decisive role of the carbene ligand on the procedure of the reaction and led to the observation of an unusual catalytic phenomenon, here called self-inhibition. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).