Reversible Heterolytic Si–H Bond Activation by an Intramolecular Frustrated Lewis Pair

Abstract

The intramolecular frustrated P/B Lewis pair Mes 2 PCH 2 CH 2 B(C 6 F 5 ) 2 (7) reacts readily with phenylsilane by heterolytic cleavage of the Si-H bond to give the zwitterion [Mes 2 (PhH 2 Si)P+CH 2 CH 2 B-H(C 6 F 5 ) 2 ] (8a), which has been fully characterized and its structure confirmed by X-ray crystal structure analysis. Variable-temperature NMR studies revealed that the reaction is reversible. Adduct 8a is the predominant species (ca. 98%) in CD 2 Cl 2 solution at low temperature (193 K), whereas at ambient temperature (299 K) it exists in a ca. 7 : 3 equilibrium with unreacted 7 and PhSiH 3 . Diphenylsilane reacted similarly with the frustrated Lewis pair 7, however, the equilibrium was found to favor the starting materials in the investigated temperature range.