Catalytic activity studies. The catalytic performance of the new, "stacked" complexes was compared with known benchmark Ru5 using a set of model reactions. First, we checked their activity in ring closing metathesis (RCM) with tetrasubstituted C-C double bond formation. For this purpose, diethyl 2,2-di(2-methylallyl)malonate (10a) was chosen as the model substrate and the time-conversion plots of its RCM reaction were constructed with 0.2 mol% of each catalyst, in toluene, at 80 °C (Figure ). All complexes exhibited high activity, affording considerable conversions within the first 30 minutes. Noteworthy, Ru5 is one of the most active catalysts designed for this reaction, and the new catalysts bear the same small N-substituents at the NHC ligands.