Pulse radiolysis studies of water-soluble tungsten hydride complexes: One-electron reduction of metal hydrides and hydrogen atom transfer reactions

The reactivity of the previously (Organometallics 2000, 19, 824-833) prepar ed hydride complexes (C5H4CO2H)L(CO)(2)WH (L = CO, PMe3) and the correspond ing metal-metal dimers [(C5H4CO2H)L(CO)(2)W](2) in pulse radiolysis studies in aqueous solution is reported. The disappearance of e(aq)(-) was monitor ed to determine the rate constants for one-electron reduction. The smallest reduction rate constant was obtained for the dianion (C5H4CO2)-(CO)(3) W2- (4.3 x 10(9) M-1 s(-1)), and the largest value (1.2 x 10(10) M-1 s(-1)) wa s observed for its conjugate acid (C5H4CO2)(CO)(3)WH-. For the PMe3-substit uted complexes, the dimer reduction rate constant was about twice as large as that for the hydride (k = 8.4 x 10(9) M-1 s(-1)). Rate constants for rea ction with CO2-, 3.2 x 10(8) (pH 5) and 3.0 x 10(7) (pH 9.7) M-1 s(-1), wer e determined for (C5H4CO2)(CO)(3)WH- and (C5H4CO2)(PMe3)(CO)(2)WH-, respect ively. Rate constants for the reactions of the hydride complexes with the c arbon-centered radical from tert-butyl alcohol and the a-hydroxy radicals f rom ethanol and 2-propanol radicals were in the ranges (0.9-4.8) x 10(8) an d (0.3-0.6) x 10(9) M-1 s(-1) for (C5H4CO2)(CO)(3)WH- and (C5H4CO2)(PMe3)(C O)(2)WH-, respectively. The transient produced in all of these reactions wa s the metal radical, which was observed to dimerize with k = 2.4 x 10(9) an d 2.2 x 10(8) M-1 s(-1) for (C5H4CO2)(CO)(3)WH- and (C5H4CO2)(PMe3)(CO)(2)W H-, respectively.