On the ROMP of 2-norbornene with an in situ ruthenium carbene complex: ESI-MS, NMR and DFT analyses

During the reaction between [{RuCl(dppb)}2-(μ-Cl)2] and ethyldiazoacetate (EDA) a neutral carbene complex was observed in situ in a methylene chloride solution, with vigorous N2 evolution. This reaction was investigated by ESI-MS analysis, which suggests the formation of a mononuclear carbene containing ruthenium complex as product, [RuCl2(dppb)(double bond; length as m-dashCHC(O)OCH2CH3]. The carbene complex was also detected by proton NMR with δ 22.8 ppm for the heteronuclear coupling, 3JHP = 7 Hz, and 31P{1H} NMR with a singlet signal at δ 30 ppm. The DFT calculation suggests a square pyramidal ruthenium structure for [RuCl2(dppb)(double bond; length as m-dashCHC(O)OCH2CH3] with 16 valence electrons and the carbene moiety trans to a vacant site. The carbene complex, generated in situ, was applied to the polymerization of 2-norbornene, achieving a wide range of turnover numbers and PDI values.