Cage Amine Superbases: Synthesis and Studies of Nona(ethylene)Hexamine and Dodeka(ethylene)Octamine

<p dir="ltr">Abstract: </p><p dir="ltr">The cage-amine molecules nona(ethylene)hexamine and dodeka(ethylene)octamine, have been prepared by coupling 1,4,7-triazacyclononane (tacn) or 1,4,7,10-tetraazacyclododecane (cyclen) to the corresponding α-chloroacetamide derivatives of these macrocycles. The formed tri- or tetra-amide cryptands were then reduced to the corresponding hexamine and octamine with borane. In all cases, the amide and amine cryptands were isolated as protonated ammonium salts, with the proton oriented to the inside of the cage molecules (i.e., endohedral). Deprotonation studies on the hexamine and octamine showed the encapsulated protons are highly inert, with no evidence of deprotonation or deuterium exchange. Detailed theoretical studies predict very high proton affinity and basicity of 1118.7 and 1086.7 kJ mol⁻¹, respectively, for dodeka(ethylene)octamine, and 1108.3 and 1083.7 kJ mol⁻¹, respectively, for nona(ethylene)hexamine, placing them among the strongest amine bases ever prepared and firmly within the realm of “superbases”.</p>