For both complexes, 16 release finishes within the first 4 h, although for Ru16 the slope is considerably steeper than for Ru17. This is in line with the hypothesis that Ru16 is a more active catalyst than Ru17 probably due to a faster initiation rate resulting from a higher trans effect of more electron donating BI*Ph NHC ligand. To further evaluate the scope and limitations of catalysts Ru16 and Ru17, several challenging cross metathesis (CM) reactions were investigated (Scheme 5). First, we studied the reaction between ethyl chrysanthemate (17) and Z-1,4-diacetoxy-2-butene (18). The challenge of this transformation lies in the low reactivity of the trisubstituted double C-C bond in 17. Noteworthy, in the example of CM of 20 with amylene ( ), the biplane-type NHC catalysts Ru16 and Ru17 gave almost quantitative conversions of 20, 93% and 91% respectively, which was 5 times higher than in the case of Ru5, reaching only 18%. Last but not least, the highly challenging 1,5-enyne metathesis of substrate 24 to obtain crowded and strained cyclobutene derivative 25 was attempted. An additional difficulty arising in this reaction is that its selectivity can be compromised by a competing homo-dimerisation side reaction and by degradation of the highly strained resulting product. We were pleased to find that catalysts Ru16 and Ru17 gave good yields of 59% and 53% respectively, whereas with Ru5 only traces of product were observed, which amounted to 6% yield. Interestingly, similarly to the case of the RCM reaction of 15a, in this example, catalyst Ru16 performed visibly better than its fluorinated counterpart Ru17, which we attribute to Ru16 higher activity. Remarkably, the use of the new catalysts allowed for a two-fold diminution in catalyst loading compared to the general-purpose SIMes complex Ru2 used at 20 mol% loading. It should be noted that some differences in solubility were noticed at such high catalyst loadings. In this respect, complexes Ru5 and Ru16 performed better in toluene, which was able to dissolve them at the reaction temperature, while perfluorotoluene could not solubilise them entirely at this temperature. On contrast, complex Ru17 dissolves better in perfluorotoluene, therefore this solvent was used in a test, in which Ru16 gave also a similarly satisfactory yield of product 25.