A six-coordinated cationic ruthenium carbyne complex with liable pyridine ligands: synthesis, structure, catalytic investigation, and DFT study on initiation mechanism

A novel six-coordinated high-valence cationic ruthenium carbyne complex bearing two liable pyridine ligands was prepared in high yield by the reaction of the ruthenium-based complex (IMesH2)(Cl)2(C5H5N)2RuCHPh [IMesH2=1,3-dimesityl-4,5-dihydroimida-zol-2-ylidene] with excess iodine as an oxidant in CH2Cl2 at 25 °C under N2. The new ruthenium carbyne-based complex shows moderate to good catalytic activity for ring-closing metathesis reactions. Importantly, no double bond isomerization by-product was produced at elevated reaction temperatures (100 °C–137 °C) in the reaction catalyzed by the synthesized ruthenium carbyne complex. A mechanism involving the in situ conversion of the ruthenium carbyne through the addition of an iodide to the carbyne carbon was also proposed, and DFT calculations were performed to explain the initiating mechanism.

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