Stabilization of propene molybdenum and tungsten half-sandwich complexes by intramolecular coordination of a...

This study reports the stabilizing effect of an intramolecularly coordinated thioether function in propene complexes of the general formula [{η⁵:κS-C₅H₄(CH₂)₂SR}M(CO)₂(η²-C₂H₃Me)][BF₄] (M = Mo, W; R = Et, Ph). They are formed by protonation of allyl analogues [{η⁵-C₅H₄(CH₂)₂SR}M(CO)₂(η³-C₃H₅)] by tetrafluoroboric acid in non-coordinating solvents. In contrast to analogues with unsubstituted Cp ligands, these propene complexes are isolable in a pure form and characterized by NMR spectroscopy. The molybdenum compounds are stable at low temperature and the propene ligand can easily be exchanged by thioethers or acetonitrile. Several representatives of the reaction products were characterized by X-ray structure analysis. The stabilization effect in tungsten complexes [{η⁵:κS-C₅H₄(CH₂)₂SR}W(CO)₂(η²-C₂H₃Me)][BF₄] (R = Et, Ph) was unusually high. The compounds are long-term stable at room temperature and do not undergo ligand exchange reactions even with strong chelators such as 1,10-phenanthroline. The molecular structure of the tungsten propene complex was confirmed by X-ray diffraction analysis on a single crystal.