The first thioallenylidene complexes from ruthenium-butatrienylidene intermediates

Ruthenium-butatrienylidene cations trans-[Cl(L-2)(2)Ru=C=C= C=CH2](+) are k ey intermediates in the synthesis of the first thioallenylidene complexes t rans-[Cl(L-2)(2)Ru=C=C=C(SR)R'](+) (L-2 = dppm, R = Et, R' = Me: 3a, L-2 = dppm, R = Me, R' = C4H7: 3b, L-2 = dppe, R = C3H5, R' = C4H7: 3c). Spectros copic and electrochemical data for 3a-c are presented and are compared with those of their aminoallenylidene analogues, Aminoallenylidene complexes ar e best represented by the iminiumalkynyl resonance form, while a true cumul ene description is much more appropriate for thioallenylidene complexes 3a- c. Based on a combination of spectroscopic and electrochemical data, we pre sent evidence that the NMR shifts of the carbon atoms of the unsaturated li gand in these allenylidene complexes are correlated to the HOMO-LUMO gap. I n situ EPR-, UV/Vis-, and IR-spectro-electrochemistry reveals that the one- electron oxidation occurs at the metal center, while reduction occurs at th e carbon-heteroatom terminus.