d¹ Oxosulfido-Mo(V) Compounds: First Isolation and Unambiguous Characterization of an Extended Series

Reaction of Tp^<i>i</i>PrMo^VIO­S­(OAr) with cobaltocene in toluene results in the precipitation of brown, microcrystalline oxosulfido-Mo­(V) compounds, [CoCp₂]­[Tp^<i>i</i>PrMo^VO­S­(OAr)] (Cp^– = η⁵-C₅H₅^–, Tp^<i>i</i>Pr^– = hydrotris­(3-isopropylpyrazol-1-yl)­borate, OAr^– = phenolate or 2-^<i>s</i>Bu, 2-^<i>t</i>Bu, 3-^<i>t</i>Bu, 4-^<i>s</i>Bu, 4-Ph, 3,5-^<i>s</i>Bu₂, 2-CO₂Me, 2-CO₂Et or 2-CO₂Ph derivative thereof). The compounds are air- and water-sensitive and display ν­(MoO) and ν­(Mo‐ ‐ ‐S) IR absorption bands at ca. 890 and 435 cm^–1, respectively, 20–40 cm^–1 lower in energy than the corresponding bands in Tp^<i>i</i>PrMoO­S­(OAr). They are electrochemically active and exhibit three reversible cyclovoltammetric waves (<i>E</i>(Mo^VI/Mo^V) = −0.40 to −0.66 V, <i>E</i>([CoCp₂]⁺/CoCp₂) = −0.94 V and <i>E</i>(CoCp₂/[CoCp₂]⁻) = −1.88 V vs SCE). Structural characterization of [CoCp₂]­[Tp^<i>i</i>PrMoOS­(OC₆H₄CO₂Et-2)]·2CH₂Cl₂ revealed a distorted octahedral Mo­(V) anion with MoO and Mo‐ ‐ ‐S distances of 1.761(5) and 2.215(2) Å, respectively, longer than corresponding distances in related Tp^<i>i</i>PrMoO­S­(OAr) compounds. The observation of strong S­(1s) → (S­(3p) + Mo­(4d)) S K-preedge transitions indicative of a d¹ sulfido-Mo­(V) moiety and the presence of short MoO (ca. 1.72 Å) and Mo‐ ‐ ‐S (ca. 2.25 Å) backscattering contributions in the Mo K-edge EXAFS further support the oxosulfido-Mo­(V) formulation. The compounds are EPR-active, exhibiting highly anisotropic (Δ<i>g</i> 0.124–0.150), rhombic, frozen-glass spectra with <i>g</i>₁ close to the value observed for the free electron (<i>g</i>_e = 2.0023). Spectroscopic studies are consistent with the presence of a highly covalent Mo‐ ‐ ‐S π* singly occupied molecular orbital. The compounds are highly reactive, with reactions localized at the terminal sulfido ligand. For example, the compounds react with cyanide and PPh₃ to produce thiocyanate and SPPh₃, respectively, and various (depending on solvent) oxo-Mo­(V) species. Reactions with copper reagents also generally lead to desulfurization and the formation of oxo-Mo­(V) or -Mo­(IV) complexes