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Calorimetric Study of the Activation of Hydrogen by Tris(pentafluorophenyl)borane and Trimesitylphosphine

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journal contribution
posted on 27.10.2017, 00:00 by Adrian Y. Houghton, Tom Autrey
The mechanism of H2 heterolysis by the frustrated Lewis pair of B­(C6F5)3 and P­(mes)3 was investigated by isothermal reaction calorimetry in the temperature range from 30 to 90 °C. The experimental heat curves were modeled in Berkeley Madonna to obtain both kinetic and thermodynamics data simultaneously. The H2 activation reaction is treated as a single, termolecular step with a rate constant of 0.61 M–2 s–1 at 303 K with an exothermic enthalpy of reaction, ΔHH2 = −141 kJ/mol. An Eyring analysis gave activation parameters of ΔH = 13.6(9) kJ mol–1 and ΔS = −204(85) J K–1 mol–1. Using D2 gas in place of H2 gas provided an opportunity to measure the relative rates of D2 versus H2 heterolysis to yield a the kinetic isotope effect, KIE = 1.1(1).