Allosteric Differentiation of Al(I) Reactivity

Abstract The dimeric potassium alumanyl, [{SiN Dipp }AlK] 2 ({SiN Dipp } = {CH 2 SiMe 2 N(Dipp)} 2 ; Dipp = 2,6‐ i ‐Pr 2 C 6 H 3 ), reacts with two equivalents of PhC≡CR (R = Ph or SiMe 3 ) with the exclusive formation of the aluminacyclopropene derivatives, [{SiN Dipp }Al{η 2 ‐C 2 (R 1 )(R 2 )}]. 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.