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[References: 24 tit.]

We report on the synthesis and characterization of SIMes/PCy3 mixed ligand coordinated second generation ruthenium catalysts, bearing various 3-alkyl-1-indenylidene ligands, denoted as RuCl2(3-alkyl-1-indenylidene)(SIMes)(PCy3), in which alkyl is isopropyl (4f), tert-butyl (4g) or cyclohexyl (4h). The characterization of complexes 4f-4h was performed using infrared spectroscopy, elemental analysis, high-resolution mass spectrometry and NMR spectroscopy. In addition, the configuration of complexes 4f and 4g was analyzed using single crystal X-ray diffraction analysis. The catalytic activities of 4f-4h were evaluated in the olefin metathesis reaction of the ring-closing metathesis of diethyl diallylmalonate, and the ring-opening metathesis polymerization of cis,cis-cyclooctadiene in comparison with the reference complex 4a. The results reveal that all complexes 4a and 4f-4h exhibit similar catalytic activity towards the tested substrates. Careful analysis of the catalyst performance and single-crystal X-ray diffraction data of the obtained complexes reveals that the steric modification on the 3-alkyl group shows a negligible influence on the ligand congestion around the ruthenium center as well as on the catalytic activities in the metathesis reactions.