Stopped-Flow Kinetic Study of the Reaction of (P(C6H11)3)2W(CO)3(L) (L = H2, D2, and N2) with Pyridine. Kinetic Resolution of Reaction of Dihydride versus Molecular Hydrogen Complexes.

Article abstract of DOI:10.1021/ja00192a021

The rates of reaction of (P(C6H11)3)2W(CO)3(L) (L = H2, D2, and N2) with pyridine have been studied by stopped-flow kinetics.The molecular nitrogen system shows simple first-order loss of N2 with a rate constant of 75 s^-1 at 25 deg C and an activation energy of 17.8 +/- 0.7 kcal/mol.The rate of reaction of the intermediate (P(C6H11)3)2W(CO)3 with N2 gas is 5.0 +/- 1.0 x 1E5 M^-1 s^-1 at 25 deg C in toluene solution.Reactions of the hydrogen and deuterium complexes are complicated due to the presence of both molecular hydrogen (deuterium) and dihydride(dideuteride) complexes.These data are resolved and interpreted in terms of a rapid loss of molecular hydrogen (k = 469 s^-1 for H2 and 267 s^-1 for D2 at 25 deg C, ΔH(excit.) = 16.9 +/- 2.2 kcal/mol for H2 and 16.2 +/- 1.1 kcal/mol for D2).The hydride complex, which is present in ca. 30percent, reacts an order of magnitude slower than the molecular hydrogen complex (k = 37 s^-1 for H2 and 33 s^-1 for D2 at 25 deg C, ΔH(excit.) = 14.4 +/- 0.5 kcal/mol for H2 and 14.7 +/- 0.8 kcal/mol for D2).The rate of addition of H2 to (P(C6H11)3)2W(CO)3 is calculated to be 2.2 +/- 0.3 x 1E6 M^-1 s^-1 at 25 deg C.These data are combined with earlier thermodynamic measurements to generate a reaction profile for binding and oxidative addition of hydrogen to the complex (P(C6H11)3)2W(CO)3.