Functionalization of polyoxomolybdates: the example of nitrosyl derivatives

Nitrosyl derivatives of polyoxomolybdates have been synthesized and characterized by X-ray diffraction. Most of them contain the Mo^II(NO)³⁺ unit and their structures are related to the following structural types: Lindqvist, Keggin and decatungstate W₁₀O₃₂]^4–. Reductive nitrosylation of (NBu₄)₄-Mo₈O₂₆] by hydroxylamine in methanol yields (NBu₄)₂Mo₅O₁₃(OMe)₄(NO){Na(MeOH)}]. 3MeOH, which is a versatile reagent yielding a variety of derivatives (i) by the transformation of Mo₅O₁₃(OMe)₄(NO)]^3– into Mo₆O₁₈(NO)]^3– in acetonitrile, (ii) by the formation of PMo₁₂O₃₉(NO)]^4– by reaction of Mo₅O₁₃(OMe)₄(NO)]^3– with PMO₁₂O₄₀]^3– in basic condition and (iii) by the formation of mixed valence Mo^VI/Mo^V/Mo^II decamolybdates Mo₁₀O₂₄(OMe)₇(NO)]^2–, Mo₁₀O₂₅(OMe)₆(NO)]^– and Mo₁₀O₂₀(OMe)₉(NO)₃]^2– by chemical reduction of Mo₅O₁₃(OMe)₄(NO)]^3–; Mo^II is localized while Mo^V are delocalized in the first two species but localized in the third. The unique ligating properties of Mo₅O₁₃(OMe)₄(NO)]^3– have been documented: this species acts as a tetradentate ligand in Ce{Mo₅O₁₃(OMe)₄(NO)}₂]^2–, a symmetrically tetraligating ligand in Rh₂Cp*₂(-Br){-Mo₅O₁₃(OMe)₄(NO)}] and a bidentate ligand in Mo₅O₁₃(OMe)₄(NO){RhCp*(H₂O)}]^–. Some polyoxomolybdates of the type Mo₅(NO)₂O₁₂{RC(NH₂)NHO}₂{RC(NH)NO}₂]^2–, which contain the Mo⁰(NO) ₂ ²⁺ unit, have also been characterized.