However, the reaction catalysed by Ru5 reached its limits at a significantly lower conversion than that recorded with Ru16 and Ru17. This can be attributed to a more stable 14-e -catalytic species formed from the latter catalysts versus those generated from Ru5. Interestingly, although Ru16 gave higher conversions than Ru17 within the first hour of the reaction, after this point the trend reversed, leading to 96% conversion with Ru17 versus 91% with Ru16 after 5 hours (and 72% for the benchmark Ru5). To further examine the differences in catalyst productivity, the previously described reaction of 10a was reattempted at two times lower catalyst loading of 0.1 mol% (Scheme 4). The trend observed earlier was maintained and Ru5 gave a rather poor conversion for such reaction (50%), whereas Ru16 and Ru17 gave much higher conversions of 81% and 92%, respectively. The three BIPh-type catalysts were further tested in five more challenging RCM reactions featuring tetrasubstituted double C-C bond formation. Similar was the case of the formation of the sixmembered malonate 11b and five-membered tosylamide 13b where Ru16 and Ru17 gave up to 32 percentage points (%p) higher substrate conversions compared to Ru5. The fluorinated complex Ru17 slightly but noticeably outperformed Ru16 in the two latter reactions. The superiority of the new catalysts Ru16 and Ru17 was even more pronounced in the more challenging formation of a less thermodynamically favoured seven-membered ring (compounds 12b and 14b). In these latter cases, a much higher catalyst loading of 2 mol% with malonate 12a and 1 mol% with tosylamide 14a was required to reach suitable conversions , and it is worth noting that Ru16 and Ru17 gave conversions 4-8 times higher than Ru5. Again, Ru17 was slightly better than Ru16 which overall correlates with the observed trend in stability tests. %p percentage point difference from Ru5 in a substrate conversion, determined by gas chromatography. The reaction was conducted for 8 h and by-product 15a' was formed (see Figure ). b Improvement observed in the formation of the main product 15b by replacing Ru5 with Ru16 or Ru17.