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.