The first artificially made set of electron acceptors is presented that are derived from a unique platform Cs[3,3'-Co(C(2)B(9)H(11))(2)], for which the redox potential of each differs from its predecessor by a fixed amount. The sequence of electron acceptors is made by substituting one, two, or more hydrogen atoms by chlorine atoms, yielding Cs[3,3'-Co(C(2)B(9)H(11-y)Cl(y))(C(2)B(9)H(11-z)Cl(z))]. The higher the number of chlorine substituents, the more prone the platform is to be reduced. The effect is completely additive, so if a single substitution implies a reduction of 0.1 V of the redox potential of the parent complex, then ten substitutions imply a reduction of 1 V.

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Step by step: The cluster [3,3'-Co(1,2-C(2)B(9)H(11))(2)](-) is an excellent platform for making a stepwise tunable redox potential system by dehydroiodination. With the addition of up to eight iodine substituents (purple; see picture), there is a fall in the E(1/2)(Co(III)/Co(II)) value from -1.80 V to -0.68 V (vs. Fc(+)/Fc; Fc = ferrocene). A practical application of this tunability has been observed in the growth of polypyrrole.

Reactivity studies of Li/Cl phosphinidenoid W(CO) 5 complexes 2a,b toward various iodine compounds are reported. Transiently generated complexes 2a,b yielded no selective reactions with 3-, 9-, and 9,12-diiodo o-carbaboranes 3a-c, whereas clean transfer-iodination reaction occurred with C-iodo-substituted o-carbaboranes 3d,e, thus giving chloro(iodo)phosphane complex 6a in the case of 2a. Complex 2a was also reacted with iodo(phenyl)acetylene to yield complexes 6a, 8, and 9 in competing reactions. An independent pathway to chloro(iodo)phosphane complexes 6a,b was reaction of complexes 2a,b with elemental iodine at low temperature. All compounds were unambiguously characterized by elemental analysis, multinuclear NMR, IR, MS studies, and, in the case of 6a and 9, single-crystal X-ray diffraction.

This work was supported by the Generalitat de Catalunya (2009/ SGR/00279) and the Ministerio de Ciencia e Innovación (CTQ2010-16237). A. Pepiol thanks the CSIC for a JAE grant and M. Lupu thanks the MICINN for a FPU grant. A. Pepiol and M. Lupu are enrolled in the UAB PhD program. We thank Mireia Ruis and Elena Marchante for performing the electrochemical tests. Supporting information for this article is available on the WWW under http://dx.