We here report on the stability and catalytic activity of new indenylidene-Schiff base-ruthenium complexes 3a-f through representative cross-metathesis (CM) and ring-closing metathesis (RCM) reactions. Excellent activity of the new complexes was found for the two selected RCM reactions; prominent conversion was obtained compared to the commercial Hoveyda-Grubbs catalyst 2. Moreover, excellent results were obtained for a standard CM reaction. Higher conversions were achieved with one of the indenylidene catalysts compared with HoveydaGrubbs catalyst. Unexpectedly, an isomerization reaction was observed during the CM reaction of allylbenzene. To the best of our knowledge, isomerization reactions in this model CM reaction in closed systems have never been described using first generation catalysts, including the Hoveyda-Grubbs catalyst. The first model CM reactions as well as the RCM reactions have been monitored using 1 H NMR. The course of the CM reaction of 3-phenylprop-1-ene (8) and cis-1,4-diacetoxybut-2-ene (9) was monitored by GC. The isomerization reaction was studied by means of GC-mass spectrometry and in situ IR spectroscopy. All catalysts were structurally characterized by means of 1 H, 13 C, and 31 P NMR spectroscopy.