Cyclopentadienyl- and methylcyclopentadienyl-vanadium complexes containing chalcogen bridges: dechalcogenation to pseudocubane clusters

In extension of previous studies with pentamethylcyclopentadienyl (Cp{black star}, η⁵-C₅Me₅) vanadium complexes, decarbonylations in the presence of elemental chalcogens of the halfsandwich compounds CP(′)V(CO)₄ and CP(′)V(CO)₃L (L SMe₂, MeCN) containing either the unsubstituted cyclopentadienyl (Cp, η₅-C₅H₅) or the monomethyl-substituted (Cp′, η⁵-C₅H₄Me) cyclopentadienyl ring ligand have been investigated. (The notation Cp(′) indicates that both the unsubstituted (Cp) and the monomethyl-substituted (Cp′) cyclopentadienyl complexes were used.) The main products obtained from CP(′)V(CO)₃L and an excess of chalcogen were binuclear pentachalcogenides CP(′₂V₂E₅ (bd1) (E S, Se) and oxo-tritellurides Cp(′)₂V₂E₃O (bd4) (E Te), respectively. Oxygen-containing side-products such as Cp{black star}₂V₂E₃O (E S, Se), CP′₂V₂S₄O and Cp′VO(S₅ were isolated from the reactions starting from CP′V(CO)₄. Chalcogen abstraction from 1 by use of one equivalent of tri(n-butyl)phosphane (PⁿBU₃) gave the tetrachalcogenides Cp(′)₂V₂E₄ (2), while further addition of PⁿBu₃ gave pseudocubane clusters Cp(′)₄V₄E₄ (7) (E S, Se). Small amounts of trisulfides CP(′)₂V₂S₃ (3) were observed by ⁵¹V NMR spectroscopy in solutions of 1 and 2 in the presence of PⁿBu₃. Binuclear tetracarbonyl-dichalcogenides Cp(′)₂V₂(CO)₄E₂ (6) (E S, Te) were made by treating solutions of CP(′)V(CO)₃(SMe₂) with H₂S and by photolysing CP(′)V(CO)₄ in the presence of either H₂S or TePⁿ Bu₃. The reactions Of Cp′₂V₂(CO)₄S₂ (6a′) with an excess of an oligochalcogenide Na₂E₅ (E Se, Te) gave the mixed-chalcogenide complexes Cp₂V₂E₂S₂ (E Se (2d′) and Te (2f′)), which react with two equivalents of PⁿBu₃ or NiCp₂ to the pseudocubane cluster Cp′₄V₄S₄ (7a′). Thermal decarbonylation of the tetracarbonyl-dichalcogenides Cp(′)₂V₂(CO)₄E₂ (6) in toluene solution gave the tetranuclear clusters Cp(′)₄V₄E₄ (7) (E S, Te) directly. The analogous pentamethylcyclopentadienyl compounds Cp{black star}₄V₄E₄ (7{black star}) (E S, Te) were also prepared. The spectroscopic data for the new CpV and Cp′V complexes are compared with those of the corresponding Cp{black star}V compounds.