Reactivity of a 17e Organometallic Radical in Aqueous Solution

Laser flash photolysis of [(C[sub 5]H[sub 4]CO[sub 2])W(CO)[sub 3]][sub 2] in aqueous solution at 460-532 nm induces homolysis of the metal-metal bond with formation of the 17e radical (C[sub 5]H[sub 4]CO[sub 2[minus]])W(CO)[sub 3]. The rate constant for its dimerization is 3.0 x 10[sup 9] L mol[sup [minus]1] s[sup [minus]1] at 23[degree]C. The radical reacts with haloacetate ions, pseudohalo- and halometal complexes by atom transfer. The reactivity trend is normal (RI > RBr > RCl). The reaction between this radical with t-BuOOH in water occurs similarly with a rate constant of 1.37 x 10[sup 6] L mol[sup [minus]1] s[sup [minus]1]. For electron-transfer reactions, the radical acts as both reductant and oxidant. It oxidizes tetramethylphenylenediamine to TMPD[sup [sm bullet]+] in aqueous solution with a rate constant of 1.49 x 10[sup 7] mol[sup [minus]1] s[sup [minus]1]. The radical reduces MV[sup 2+] and Fe(CN)[sub 6][sup 3[minus]] to MV[sup [sm bullet]+] and Fe(CN)[sub 6][sup 4[minus]] with rate constants of 2.0 x 10[sup 6] and 6.06 x 10[sup 7] L mol[sup [minus]1] s[sup [minus]1], respectively. The phosphine Ph[sub 2]PPhSO[sub 3]Na accelerates the reaction of the radical with MV[sup 2+] very mildly. This may bear on the question of whether the tungsten-phosphine adduct is a species with 19 valence electrons, a slipped cyclopentadienyl ring, or a phosphoranyl radical. 32 refs., 2 figs., 4 tabs.