Kinetics of protonation of tungsten hydrides WH(CO)2(NO)L2 by weak OH-acids

The kinetics of protonation of tungsten hydrides WH(CO)₂(NO)L₂ (1, L = PMe₃, PEt₃, P(OPri)₃, PPh₃) by weak OH-acids (PhOH, (CF₃)₂CHOH, (CF₃)₃COH) in hexane was studied by IR spectroscopy. The study of the reactions of compounds 1 with OH-acids at 190–270 K revealed that the first step involves the formation of dihydrogen-bonded W(CO)₂(NO)L₂(H)...HOR complexes. When the temperature increases to ambient, the proton transfer and evolution of molecular hydrogen occur, affording the final products: organyloxy derivatives W(OR)(CO)₂(NO)L₂. The study of the kinetics at 298 K found that the proton transfer is the rate-determining step. The rate constants k _app are 2.2·10⁻⁵–6.3·10⁻⁴ s⁻¹, and the free activation energies are ΔG ^≠ _298K = 22–23 kcal mol⁻¹. The rate constants depend on the proton-accepting properties of the hydride and the acidic properties of the OH-proton donor and increase in the same order as the enthalpy of hydrogen bond formation. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 837–841, May, 2007.