First Detection of a Ruthenium–Carbene–Resorc[4]arene Complex During the Progress of a Metathesis Reaction

For the first time we describe the detection of a ruthenium‐carbene‐resorc[4]arene complex produced, as a key intermediate, during an olefin metathesis reaction carried out on a resorc[4]arene bicyclic olefin with [Ru(=CHPh)Cl 2 (PCy 3 ) 2 ] Grubbs first‐generation (G 1 ST) catalyst. The complex was identified by using high‐resolution (600 MHz) 1 H, 31 P NMR and DOSY spectroscopy, in a non‐invasive fashion. The singlet at δ = 19.98 ppm ( 1 H NMR), attributed to the alkylidene proton in the G 1 ST catalyst and that at δ = 53.37 ppm ( 31 P NMR), attributed to the phosphorus atom coordinated with the metal, were selected as probes for a kinetic analysis. The intensity of these signals decreased at the expense of the singlets at 19.26 ( 1 H NMR) and 52.68 ppm ( 31 P NMR), diagnostic for the formation of the ruthenium‐carbene‐resorc[4]arene complex 3a [Ru]. The resorc[4]arene activated olefin proved to behave as a key propagating species leading to oligomers according to a ROMP pathway.