Reversible heterolytic Si-H bond activation by an intramolecular frustrated Lewis pair

摘要

The intramolecular frustrated P/B Lewis pair Mes _2PCH _2CH _2B(C _6F _5) _2 (7) reacts readily with phenylsilane by heterolytic cleavage of the Si-H bond to give the zwitterion [Mes _2(PhH _2Si)P +CH _2CH _2B-H(C _6F _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 _2Cl _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.