Isotopic probes for ruthenium-catalyzed olefin metathesis

Abstract

Routes are described to previously unreported first- and second-generation Grubbs metathesis catalysts bearing a ¹³C label at the key benzylidene or methylidene site. Improved syntheses of the ²H-labelled isotopologues are also presented. Labelling at the alkylidene position is important because it provides unique, direct information about changes at the active site of the catalyst, and the fate of the [Ru]CHR ligand during catalyst deactivation. A case study demonstrates the power of ¹³C-labelling in tracking the methylidene moiety in amine-induced decomposition of the second-generation complex RuCl₂(PCy₃)(H₂IMes)(¹³CH₂). Also reported is the solubility of ethylene in C₆D₆ and CD₂Cl₂, measured at 296 ± 1.5 K and 101.0 ± 0.8 kPa.