Electron-Transfer Equilibria for Contact Ion Pairs

The establishment of electron-transfer equilibria is allowed by the unique stabilizations inherent in the organometallic anion TpMo(CO)3 [where Tp = hydridotris(3,5-dimethylpyrazolyl)borate] (85), in which the 17-electron radical (m20 is persistent (56). Since other members of the group VIB metals, namely, TpW(CO)3 and TpCr(CO)3-, are also available (87), this triad of anions enables the structural effects to be systematically examined, 

Electron-transfer equilibria of the organometallic anions TpM(CO)3- can be examined by coupling them with a graded series of triarylpyrylium cations (TaP+) for which 1-electron reduction potentials are known to be strongly dependent on the substituents (88). The evaluation of the constant K for the electron-transfer equilibrium in Eq. (39) requires the quantitative analysis of the anionic organometallic redox couple in Eq. (38), as well as that of triarylpyrylium cation. 

Spectral Characterization of TpM(CO)3 Anions and Their 17-Electron Radicals, Where M Is Mo, W, and Cr 

Each TpM(CO)3 anion is readily identified by its characteristic IR spectrum consisting of two carbonyl bands corresponding to the symmetric A i and the antisymmetric E stretching frequencies for idealized C3v symmetry (37). The isostructural molybdenum, tungsten, and chromium de- 

The electrochemical reduction of the triarylpyrylium cations can be examined in dichloromethane solution by cyclic voltammetry. The reversible one-electron potentials for the cation reduction, 

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