Isovalent and mixed-valent molybdenum complexes containing MoV(μ-E)(μ-S2)MoV/IV (E = O, S) core units

Abstract

The reactions of TpiPrMoO(SR)(NCMe) (TpiPr = hydrotris(3-isopropylpyrazolyl)borate) with propylene sulfide in toluene result in the formation of the diamagnetic, isovalent Mo(V) complex, [TpiPrMoVO]2(μ-S)(μ-S2). This complex and its previously reported μ-oxo analog, [TpiPrMoVO]2(μ-O)(μ-S2), react with cobaltocene to produce one-electron-reduced, mixed-valent complexes, [CoCp2][{TpiPrMoIV,VO}2(μ-E)(μ-S2)] (E = S or O, respectively). All complexes have been isolated and characterized by microanalysis, mass spectrometry, IR and 1H NMR or EPR spectroscopies, and X-ray crystallography. Neutral [TpiPrMoVO]2(μ-S)(μ-S2) exhibits a pseudo-C2 symmetric structure, with distorted octahedral anti oxo-Mo(IV) centers coordinated by TpiPr and linked by μ-sulfido and μ-disulfido ligands. A similar structure is adopted by the anion in mixed-valent [CoCp2][{TpiPrMoIV,VO}2(μ-S)(μ-S2)]; this compound adopts a hexagonal, supramolecular structure with columns of tight ion-pairs with (μ-S2)...CoCp2+ interactions, interconnected through weaker (μ-S2)...CoCp2+ contacts to three neighboring columns. The structure contains large interstitial voids filled with lattice solvent molecules. EPR investigation of the mixed-valent complexes gave rise to unusually broad signals with no evident hyperfine splitting. The synthesis and characterization of a number of cis-dioxo-Mo(VI) precursors are also reported.