Direct observation of a cationic ruthenium complex for ethylene insertion polymerization

Abstract

We report here the first direct observation of a cationic ruthenium complex catalyzing ethylene insertion polymerization. An arene-tethered ruthenium complex (η⁶-C₆H₅(CH₂)₃SCH₃RuCl₂) (3) was synthesized and shown to be able to catalyze ethylene polymerization upon activation with AlMe₂Cl. For mechanistic studies, we synthesized the homologous dimethylated η⁶-C₆H₅(CH₂)₃SCH₃Ru(CH₃)₂ (4) complex, which upon activation with the Brookhart acid ([H(Et₂O)₂]⁺ [BAr′₄]⁻) was also active for ethylene insertion polymerization. ¹H-NMR and mass spectrometry (MS) studies provide direct evidence for a ruthenium cationic [η⁶-C₆H₅(CH₂)₃SCH₃Ru(oligomer)]⁺ complex as the active species during polymerization. This has unambiguously shown for the first time a ruthenium complex as the active species for catalyzing olefin insertion polymerization.