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

Abstract

Reactions of the metal hydride complexes Cp*(CO)2MH (M = Fe, Ru, Os) with Ph3C+BF4- in CH2Cl2 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 CH2Cl2 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 activ...