The stability of the two newly obtained biplane-type NHC ruthenium complexes Ru16 and Ru17 was then quantitatively monitored and compared with the benchmark Ru5. Since the NHC ligand remains coordinated to the metal centre throughout the entire catalytic cycle, the differences in complexes' stability should directly translate to the stability of actual propagating species, thus conveying their effectiveness in catalysis. Gratifyingly, Ru16 and Ru17 remained perfectly unchanged for approximately three weeks in solution at ambient temperature, while Ru5 slowly degraded to around 50% of the initial amount (Figure , left). This result confirmed our previous observation that upon isolation the top-covered complexes Ru16 and Ru17 are considerably more stable than Ru5. Furthermore, the differences in stability were even more pronounced at higher temperature (Figure , right), where Ru5 disappeared completely after about 27 hours, while Ru16 and Ru17 were still detectable even after more than 100 hours in solution at 80 °C. Furthermore, the elevated temperature allowed to distinguish Ru16 from Ru17 in terms of stability, with the Ru17 resulting the most stable catalyst.