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Dalton Transactions

The international journal for inorganic, organometallic and bioinorganic chemistry



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Dalton Trans., 2009, 9746 - 9758, DOI: 10.1039/b912986c

Thiolates vs. halides as -donors: the redox-active alkyne complexes [M(SR)L(-RCCR)L] {M = Mo or W, L = CO or P(OMe)3, L = -C5H5 and Tp}

Christopher J. Adams, Angharad Baber, Supakorn Boonyuen, Neil G. Connelly, Beatriz E. Diosdado, Anob Kantacha, A. Guy Orpen and Elena Patrón

The cyclic voltammograms of the alkyne complexes [M(SR)L(-RCCR)(-C5H5)] (M = Mo or W, R = Me or Ph, R = Me or Ph) show two oxidation processes. Both are irreversible for the stereochemically rigid carbonyls (L = CO) but the first is reversible for the fluxional phosphites {L = P(OMe)3}; the paramagnetic monocations [M(SPh){P(OMe)3}(-MeCCMe)(-C5H5)]+ were detected by ESR spectroscopy after in situ chemical one-electron oxidation. By contrast, the hydrotris(pyrazolyl)borate analogues [W(SR)(CO)(-PhCCPh)Tp] {R = Me or Ph, Tp = hydrotris(3,5-dimethylpyrazolyl)borate} are oxidised in two reversible steps to the corresponding mono- and dications; the redox pair [W(SPh)(CO)(-PhCCPh)Tp]z (z = 0 and 1+) has been structurally characterised. A comparison of the redox potentials for the oxidation of [W(SR)(CO)(-PhCCPh)Tp] with those of the halide analogues [WX(CO)(-PhCCPh)Tp] suggests that the factors which give rise to the inverse halide order for the latter may not operate for the thiolates, which appear to be the better -donors in all three redox states [WL(CO)(-PhCCPh)Tp]z (L = halide or thiolate, z = 0, 1+ and 2+).

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