N-Geminal P/Al Lewis Pair–Alkyne Dipolar Cycloaddition to the Zwitterionic C2PNAl-Heterocyclopentene

The N-geminal P/Al Lewis pair [Ph2PN(2,6-iPr2C6H3)AlEt2]2 (1) has been prepared and studied for reaction with a series of alkynes. The reaction of 1 with RC≡CR yielded zwitterionic C2PNAl-heterocyclopentene [Ph2PN(2,6-iPr2C6H3)AlEt2](CR═CR) (R = Me (2), Ph (3)); with PhC≡CEt produced two isomers, [Ph2PN(2,6-iPr2C6H3)AlEt2](CPh═CEt) (4a) and [Ph2PN(2,6-iPr2C6H3)AlEt2](CEt═CPh) (4b); and with other alkynes generated [Ph2PN(2,6-iPr2C6H3)AlEt2](CR1═CR2) (R1, R2 = CO2Et, Ph (5); SiMe3, Ph (6); PPh2, Ph (7); SiMe3,H (8); H, EtO (9)). Natural bond orbital analysis of the charge separation of the C≡C bond of alkynes was carried out, and then, the electronic matching interaction mode between the combined Lewis acid (AlEt2) and base (PPh2) groups of 1 and the C≡C bond of such alkynes was discussed. Reactions of 1 with alkene, nitrile, and carbodiimide molecules were also carried out, and cycloaddition compounds 10–12 were produced.