Such an olefin isomerisation was already shown to result from the degradation of the metathesis catalysts, generating ruthenium-hydride species. The observed formation of 15a' stands in agreement with the previous report of Grubbs and co-workers, although this isomerisation product was not characterised there. Catalyst Ru5 offered a very poor conversion of 15a, forming 15b and 15a' in comparable amounts (15a:15b:15a'ratio of 96:1.4:2.7). Interestingly, in this example Ru16 outperformed Ru17, both in terms of conversion and selectivity toward 15b (15a:15b:15a' ratio for Ru16 reached 24:75:0.9 versus 51:44:5.4 for Ru17 after 8 hours at 80 °C).