Unfortunately, modifications in the ether substituents of the benzylidene ligand did not improve the stability of the complexes in the presence of oxygen (Table ). In each case (if the complexes were active enough to catalyse the reaction), we observed a decrease in yield between inert and air conditions by 20-30 percentage points, which is comparable to the benchmark catalysts Ru5 and Ru7 ( and 16 percentage points, respectively). To our delight, however, we found that the changes had a positive effect on the activity of some complexes, namely Ru19 and Ru21, enabling higher yields of 4aa to be obtained in both inert gas and air than those for Ru5 (see Table and). It is worth noting that for the most active complex in our series, Ru21, increasing the temperature resulted in a slight decrease in yield and selectivity, to 76% and (Z):(E) = 96:4 at 45 °C compared to 80% and (Z):(E) = 96:4 at room temperature, which can be related to its faster decomposition under these conditions (Table and). As expected complexes with SIPr ligands, despite their higher stability, gave lower conversions due to their lower activity; increasing the temperature slightly improved the yield but at the expense of selectivity. In all cases, we obtained very good Z-selectivity of around 98:2 or higher, and only Ru17 was slightly worse (96:4 under N 2 and 92:8 in air). To our surprise, Ru23 turned out to be poorly active, although its counterpart with two chloride ligands Ru16 catalysed olefin metathesis reactions already at 0 °C. . a Conditions: 2a (1 equiv.), 3a (2 equiv.), THF (degassed), rt, 4 h, glovebox. For reactions "on air", such prepared reaction setup was next taken out from a glovebox and opened. Determined by GC, tetradecane used as an internal standard. c Isolated yield. In parenthesis results taken from Ref. are given. e Reaction carried out at 60 °C. f Reaction carried out at 45 °C.