Aluminum containing molecular bowls and pyridinophanes: use of pyridine modules to access different molecular topologies

Abstract

Molecular topologies varying from simple complexes to pyridinophanes (neutral and cationic) and to bicyclic pyridinophane containing organoaluminum (Al–Me) species were synthesized by varying the relative stoichiometry of bis(trimethylsilyl)-N,N′-2,6-diaminopyridine (bap) and the reactive partner (AlMe₃). The ultimate goal of these reactions was to systematically design cyclic structures containing group 13 elements. To highlight the reaction potential of these shapes, the bowl-shaped pyridinophane was reacted with the Lewis acid, B(C₆F₅)₃, to generate a stable cationic derivative. An unprecedented bicyclic pyridinophane, [2,6-(Me₃SiN)₂C₅H₃N]₃Al₂, was obtained from the reaction of bap with AlH₃·NMe₂Et. The formation of [2,6-(Me₃SiN)₂C₅H₃N]₃Al₂ is in contrast to the known reaction between BH₃·SMe₂ and bap that afforded the syn-tetraazadibora[3.3](2,6)pyridinophane. Quantum chemical calculations have been performed to rationalize the preference for the formation of B-pyridinophane and Al-bicyclic pyridinophane and can be attributed to the nature of B–N and Al–N bonds.