ELECTRON-TRANSFER REACTIONS OF THE ORGANOMETALLIC FREE-RADICAL CPMO(CO)(3)(CENTER-DOT) WITH TRIPHENYLPYRYLIUM ION AND TRIPHENYLPYRANYL RADICAL

The title compound, a 17-electron organometallic free radical, undergo es reversible electron transfer in two steps in acetonitrile. It is ox idized by the triphenylpyrylium ion (TPP+) to [CpMo(CO)(3)MCCH(3)](+) and reduced by TPP. to [CpMo(CO)(3)](-). Three of the four rate consta nts for the forward and reverse directions of these two steps were eva luated directly by flash photolysis and stopped-flow techniques. The r esults were considered in light of data for similar reactions of [CpMo (CO)(3)](.) with TMPD(.+) and TMPD (TMPD = N,N,N',N'-tetramethyl-1,4-p henylenediamine). Notable differences were found, due entirely to the 0.55 V difference in E degrees for the two A(+)/A couples. On the othe r hand, surprising agreement was found between the rate constants for a pair of reactions that differ by 10(8) in their equilibrium constant s. Both of these rate constants are at the diffusion-controlled level. We thus conclude that the minor species [CpMo(CO)(3) . NCCH3](.) (som etimes referred to as a 19e radical), the binding constant of which is only similar to 10(-4) L mol(-1), may carry the diffusion-controlled reactions with TPP+ and TMPD(.+). Reduction to the 18e molybdenum anio n, however, does not proceed with the involvement of the coordinated s olvent.