Hydride transfer from (η5-C5Me5)(CO)2MH (M = Fe, Ru, Os) to trityl cation: Different products from different metals and the kinetics of hydride transfer

Tan Yun Cheng, R. Morris Bullock

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Reactions of the metal hydride complexes Cp*(CO)2MH (M = Fe, Ru, Os) with Ph3C+BF4- in CH2C12 were studied. Hydride transfer from Cp*(CO)2FeH to Ph3C+BF4- gives Cp*(CO)2FeFBF3. Hydride transfer from the ruthenium hydride Cp*(CO)2RuH to Ph3C+ BF4- produces the bridging hydride complex {[Cp*(CO)2Ru]2(μ-H)}+BF4 -, indicating that Cp*(CO)2RuH exhibits significant nucleophilicity in addition to hydridic reactivity of the Ru-H bond. The osmium hydride Cp*(CO)2OsH reacts with Ph3C+BF4- in CH2C12 to give a mixture of Cp*(CO)2OsFBF3 and [Cp*(CO)2Os(ClCH2Cl)]+BF4 -. The kinetics of these hydride transfer reactions were monitored by stopped-flow methods, leading to the second-order rate law -d[Ph3C+ BF4- ]/dt = k[Ph3C+BF4-] [MH]. The temperature dependence of the rate constants was determined for the iron hydride, the osmium hydride, and the osmium deuteride Cp*(CO)2OsD. Activation parameters for hydride transfer from Cp*(CO)2FeH are ΔH = 2.6 ± 0.1 kcal mol-1 and ΔS = -22.1 ± 0.4 cal K-1 mol-1; for Cp*(CO)2OsH the activation parameters are ΔH = 4.9 ± 0.1 kcal mol-1 and ΔS = -16.8 ± 0.5 cal K-1 mol-1. A kinetic isotope effect (kH/kD = 1.6 at 0 °C) was found for the reaction of Cp*(CO)2OsD. The order of kinetic hydricity is HRu > HFe > HOs. Second-order rate constants (extrapolated to 25 °C from data collected at lower temperatures) are k = 3.2 ± 105 M-1 s-1 for Cp*(CO)2OsH and k = 1.1 × 106 M-1 s-1 for Cp*(CO)2FeH; for Cp*(CO)2RuH, k > 5 × 106 M-1 s -1 is estimated at 25 °C. Rate constants were also determined for hydride transfer to Ph2(p-MeOC6H4)C+ at 25 °C: k = 1.5 × 105 M-1 s-1 for Cp*(CO)2RuH, k = 4.1 × 104 M-1 s-1 for Cp*(CO)2FeH, and k = 3.2 × 103 M-1 s-1 for Cp*(CO)2OsH.

Original languageEnglish
Pages (from-to)2325-2331
Number of pages7
Issue number11
Publication statusPublished - May 27 2002


ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Organic Chemistry
  • Inorganic Chemistry

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