Ru16 performance with Ru17 (Figure ). The difference in catalyst activity is more pronounced in this challenging RCM example, and complex Ru16 is considerably more active than Ru17 (15a:15b:15a' ratio after 1 h reached 28:71:0.3 with Ru16 versus 63:36:0.8 with Ru17). After the first hour of the reaction, the formation of 15b slows significantly, indicating that most of the catalytically active species has been spent. After that point, the formed decomposition products start to isomerise 15a, which is available in a higher quantity in the case of the reaction with Ru17. Those factors account for a higher amount of 15a' observed with Ru17 after 8 h.