Allosteric Differentiation of Al(I) Reactivity

The dimeric potassium alumanyl, [{SiN^Dipp}AlK]₂ ({SiN^Dipp} = {CH₂SiMe₂N(Dipp)}₂; Dipp = 2,6-i-Pr₂C₆H₃), reacts with two equivalents of PhC≡CR (R = Ph or SiMe₃) with the exclusive formation of the aluminacyclopropene derivatives, [{SiN^Dipp}Al{η²-C₂(R¹)(R²)}]. In contrast, reactions with an equal stoichiometry of both alumanyl and alkyne reagents provide the products of not only alkyne cycloaddition but also para-C-H activation of a phenyl substituent. Supported by a theoretical study, this outcome is judged to result from a sequence of cooperative steps and the introduction of a modicum of kinetic discrimination that is suggested to be allosteric in origin.