Ancillary ligand effects upon dithiolene redox noninnocence in tungsten Bis(dithiolene) complexes

Article abstract of DOI:10.1021/ic4009174

An expanded set of compounds of the type [W(S₂C ₂Me₂)₂L₁L₂]ⁿ (n = 0: L₁ = L₂ = CO, 1; L₁ = L₂ = CN^tBu, 2; L₁ = CO, L₂ = carbene, 3; L ₁ = CO, L₂ = phosphine, 4; L₁ = L₂ = phosphine, 5. n = 2-: L₁ = L₂ = CN^-, [6] ^2-) has been synthesized and characterized. Despite isoelectronic formulations, the compound set reveals gradations in the dithiolene ligand redox level as revealed by intraligand bond lengths, υ_CCchelate, and rising edge energies in the sulfur K-edge X-ray absorption spectra (XAS). Differences among the terminal series members, 1 and [6]^2-, are comparable to differences seen in homoleptic dithiolene complexes related by full electron transfer to/from a dithiolene-based MO. The key feature governing these differences is the favorable energy of the CO π* orbitals, which are suitably positioned to overlap with tungsten d orbitals and exert an oxidizing effect on both metal and dithiolene ligand via π-backbonding. The CN^- π* orbitals are too high in energy to mix effectively with tungsten and thus leave the filled dithiolene π* orbitals unperturbed. This work shows how, and the degree to which, the redox level of a noninnocent ligand can be modulated by the choice of ancillary ligands(s).