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)Cl2(PCy3)2] Grubbs first-generation (G1ST) catalyst. The complex was identified by using high-resolution (600 MHz) 1H, 31P NMR and DOSY spectroscopy, in a non-invasive fashion. The singlet at δ = 19.98 ppm (1H NMR), attributed to the alkylidene proton in the G1ST catalyst and that at δ = 53.37 ppm (31P 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 (1H NMR) and 52.68 ppm (31P 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.