Pulse Radiolysis Studies of Water-Soluble Tungsten Hydride Complexes:  One-Electron Reduction of Metal Hydrides and Hydrogen Atom Transfer Reactions

Abstract

The reactivity of the previously (Organometallics 2000, 19, 824-833) prepared hydride complexes (C 5 H 4 CO 2 H)L(CO) 2 WH (L ) CO, PMe 3 ) and the corresponding metal-metal dimers [(C 5 H 4 CO 2 H)L(CO) 2 W] 2 in pulse radiolysis studies in aqueous solution is reported. The disappearance of e aqwas monitored to determine the rate constants for one-electron reduction. The smallest reduction rate constant was obtained for the dianion (C 5 H 4 CO 2 )-(CO) 3 W 2-(4.3 × 10 9 M -1 s -1 ), and the largest value (1.2 × 10 10 M -1 s -1 ) was observed for its conjugate acid (C 5 H 4 CO 2 )(CO) 3 WH -. For the PMe 3 -substituted complexes, the dimer reduction rate constant was about twice as large as that for the hydride (k ) 8.4 × 10 9 M -1 s -1 ). Rate constants for reaction with CO 2 -, 3.2 × 10 8 (pH 5) and 3.0 × 10 7 (pH 9.7) M -1 s -1 , were determined for (C 5 H 4 CO 2 )(CO) 3 WHand (C 5 H 4 CO 2 )(PMe 3 )(CO) 2 WH -, respectively. Rate constants for the reactions of the hydride complexes with the carbon-centered radical from tert-butyl alcohol and the R-hydroxy radicals from ethanol and 2-propanol radicals were in the ranges (0.9-4.8) × 10 8 and (0.3-0.6) × 10 8 M -1 s -1 for (C 5 H 4 CO 2 )(CO) 3 WHand (C 5 H 4 CO 2 )(PMe 3 )(CO) 2 WH -, respectively. The transient produced in all of these reactions was the metal radical, which was observed to dimerize with k ) 2.4 × 10 9 and 2.2 × 10 8 M -1 s -1 for (C 5 H 4 CO 2 )(CO) 3 WHand (C 5 H 4 CO 2 )(PMe 3 )(CO) 2 WH -, respectively.

Brønsted–Lowry Acid Strength of Metal Hydride and Dihydrogen Complexes

“…192 Water-soluble complexes of the type [M(H 2 )(H)(dmprpe) 2 ] + (M = Fe, Ru, Os), dmprpe = P((CH 2 ) 3 OMe) 2 CH 2 CH 2 P((CH 2 ) 3 OMe) 2 , are stable in buffered aqueous solutions at pH 7. 78 The osmium trihydride cations [OsH 3 L 4 ] + , L = PPh 2 Me, PMe 2 Ph, PMe 3 , and PEt 3 (entries 132,133,137,138,147,149), are useful acids to establish the pK a THF scale from 12 to 19. They also provide a link to Angelici's enthalpy of protonation scale in dichloroethane solvent (DCE).…”

1H NMR Studies of Ligand and H/D Exchange Reactions of cis- and trans-([14]aneN4)(H2O)RhH2+ in Aqueous Solutions

“…As the demand for environmentally friendly catalysis increases, so does the importance of aqueous organometallic chemistry. The growing list of known water-soluble organometallic compounds [1][2][3][4][5][6][7] includes some reasonably stable transition metal hydrides such as (C 5 H 4 CO 2 H)(CO) 3 WH 1 and its derivatives (C 5 H 4 CO 2 H)(CO) 2 (PMe 3 )WH and (C 5 H 4 -CO 2 H)(CO) 2 [P(OMe) 3 ]WH. A number of other hydrides are also known.…”

“…Depending on the metal, ligands, and added reactants, the hydrides will act as hydrogen atom, hydride, or proton donors. 2,[17][18][19][20][21] Under the right circumstances and in the presence of isotopically enriched solvent and/or other reagents, such reactions may lead to the H/D exchange at the metal. For example, some Ir(III) hydrides have been reported 22 to exchange hydrogen with D 2 O solvent, and IrH 2 (η 1 -SC 5 H 4 -NH) 2 (PCy 3 ) 2 exchanges H with D 2 (g) in CH 2 Cl 2 via a η 2dihydrogen intermediate.…”

“…As the demand for environmentally friendly catalysis increases, so does the importance of aqueous organometallic chemistry. The growing list of known water-soluble organometallic compounds − includes some reasonably stable transition metal hydrides such as (C 5 H 4 CO 2 H)(CO) 3 WH 1 and its derivatives (C 5 H 4 CO 2 H)(CO) 2 (PMe 3 )WH and (C 5 H 4 CO 2 H)(CO) 2 [P(OMe) 3 ]WH. A number of other hydrides are also known. − Strictly speaking, most of them are not organometallic materials in that they lack a metal−carbon bond, but they exhibit rich chemistry and engage in both stoichiometric and catalytic reactions.…”

“…The hydridicity increases with the electron-donating power of other ligands in the complex. Depending on the metal, ligands, and added reactants, the hydrides will act as hydrogen atom, hydride, or proton donors. ,− …”