The First Thioallenylidene Complexes from Ruthenium-Butatrienylidene Intermediates

Ruthenium-butatrienylidene cations trans-[Cl(L2)2Ru=C=C=C=CH2]+ are key intermediates in the synthesis of the first thioallenylidene complexes trans-[Cl(L2)2Ru=C=C=C(SR)R′]+ (L2 = dppm, R = Et, R′ = Me: 3a, L2 = dppm, R = Me, R′ = C4H7: 3b, L2 = dppe, R = C3H5, R′ = C4H7: 3c). Spectroscopic and electrochemical data for 3a–c are presented and are compared with those of their aminoallenylidene analogues. Aminoallenylidene complexes are best represented by the iminiumalkynyl resonance form, while a true cumulene description is much more appropriate for thioallenylidene complexes 3a–c. Based on a combination of spectroscopic and electrochemical data, we present evidence that the NMR shifts of the carbon atoms of the unsaturated ligand in these allenylidene complexes are correlated to the HOMO–LUMO gap. In situ EPR-, UV/Vis-, and IR-spectro-electrochemistry reveals that the one-electron oxidation occurs at the metal center, while reduction occurs at the carbon–heteroatom terminus.