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)L-2 (1, L = PMe3, PEt3, P(OPri)(3), PPh3) by weak OH-acids (PhOH, (CF3)(2)CHOH, (CF3)(3)COH) 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)L-2(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)L-2. 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 center dot 10(-5)-6.3 center dot 10(-4) s(-1), and the free activation energies are Delta G(298K)(not equal) = 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.