100995-40-2Relevant academic research and scientific papers
Rate of reaction of (P(C6H11)3)2W(CO)3 with py, P(OMe)3, PPh2Me, and 2,6-Me2py. Stopped-flow kinetic study of concerted reactions at a sterically crowded metal center
Gonzalez, Alberto A.,Zhang, Kai,Hoff, Carl D.
, p. 4285 - 4290 (2008/10/08)
The rate of reaction of the complexes (P(C6H11)3)2W(CO)3 and (P(C6D11)3)2W(CO)3 with P(OMe)3 have been measured by stopped-flow kinetics. At 25°C the hydrogen-substituted complex follows second-order kinetics with k = 5.45 × 104 M-1 s-1 and ΔH≠ = 4.2 kcal/mol. An inverse kinetic isotope effect is observed with k(H)/k(D) = 0.87. The ligand PPh2Me reacts 3 times more slowly than P(OMe)3 and shows a larger inverse kinetic isotope effect, k(H)/k(D) = 0.78. Reaction of (P(C6H11)3)2W(CO)3 with 2,5-dimethylpyridine occurs with the rate constant 8.6 × 103 M-1 s-1 at 257deg;C, 2 orders of magnitude slower than the reaction with pyridine. The unusually high selectivity is ascribed to steric factors at the crowded metal center. New stopped-flow data at low pyridine concentrations are reported for dissociation of pyridine from the complexes (P(C6H11)3)2W(CO)3(py) and (P-(C6D11)3)2W(CO)3(py). A primary kinetic isotope effect k1(H)/k1(D) = 1.19 is observed in these reactions. These results imply that, in spite of the steric crowding at the metal center, dissociation of pyridine is assisted by partial formation of the W?H "agostic" bond in the transition state.
