Design of bis-NHC Ru-complexes featuring diarylmethylene N-substituents for olefin metathesis

New ruthenium indenylidene complexes containing N-heterocyclic carbene (NHC) ligands were synthesized and evaluated in olefin metathesis.The presence of two symmetrical saturated NHCs featuring Ndiarylmethylene fragments (R= H, OMe or F) led to robust ruthenium precatalysts with a good latency.A kinetic study was investigated showing that a thermal stimulus (>60 °C) is required to reach an efficient catalytic initiation.Interestingly, a slight electronic effect was observed depending on the presence of an electron-donating or -withdrawing group within the diarylmethylene moiety.These complexes showed good activity at 1 mol% of catalyst loading in selected ring-closing metathesis (RCM) and cross-metathesis (CM) transformations.