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) prepared hydride complexes (C₅H₄CO₂H)L (CO)₂WH (L = CO, PMe₃) and the corresponding metal-metal dimers [(C₅H₄CO₂H)L(CO)₂ W]₂ in pulse radiolysis studies in aqueous solution is reported. The disappearance of e_aq^- was monitored to determine the rate constants for one-electron reduction. The smallest reduction rate constant was obtained for the dianion (C₅H₄CO₂) (CO)₃W^2- (4.3 × 10⁹ M^-1 s^-1), and the largest value (1.2 × 10¹⁰ M^-1 s^-1) was observed for its conjugate acid (C₅H₄CO₂)(CO)₃WH^-. For the PMe₃-substituted complexes, the dimer reduction rate constant was about twice as large as that for the hydride (k = 8.4 × 10⁹ M^-1 s^-1). Rate constants for reaction with CO₂^-, 3.2 × 10⁸ (pH 5) and 3.0 × 10⁷ (pH 9.7) M^-1 s^-1, were determined for (C₅H₄CO₂)(CO)₃WH^- and (C₅H₄CO₂)(PMe₃)WH^-, respectively. Rate constants for the reactions of the hydride complexes with the carbon-centered radical from tert-butyl alcohol and the α-hydroxy radicals from ethanol and 2-propanol radicals were in the ranges (0.9-4.8) × 10⁸ and (0.3-0.6) × 10⁸ M^-1 s^-1 for (C₅H₄CO₂)(CO)₃ WH^- and (C₅H₄CO₂)(PMe₃) (CO)₂WH^-1, respectively. The transient produced in all of these reactions was the metal radical, which was observed to dimerize with k = 2.4 × 10⁹ and 2.2 × 10⁸ M^-1 s^-1 for (C₅H₄CO₂)(CO)₃ WH^- and (C₅H₄CO₂)(PMe₃) (CO)₂WH^-, respectively.