N-Geminal P/Al Lewis Pair–Alkyne Dipolar Cycloaddition to the Zwitterionic C(2)PNAl-Heterocyclopentene

[Image: see text] The N-geminal P/Al Lewis pair [Ph(2)PN(2,6-iPr(2)C(6)H(3))AlEt(2)](2) (1) has been prepared and studied for reaction with a series of alkynes. The reaction of 1 with RC≡CR yielded zwitterionic C(2)PNAl-heterocyclopentene [Ph(2)(⌜)PN(2,6-iPr(2)C(6)H(3))AlEt(2)](CR=(⌝)CR) (R = Me (2), Ph (3)); with PhC≡CEt produced two isomers, [Ph(2)(⌜)PN(2,6-iPr(2)C(6)H(3))AlEt(2)](CPh=(⌝)CEt) (4a) and [Ph(2)(⌜)PN(2,6-iPr(2)C(6)H(3))AlEt(2)](CEt=(⌝)CPh) (4b); and with other alkynes generated [Ph(2)(⌜)PN(2,6-iPr(2)C(6)H(3))AlEt(2)](CR(1)=(⌝)CR(2)) (R(1), R(2) = CO(2)Et, Ph (5); SiMe(3), Ph (6); PPh(2), Ph (7); SiMe(3),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 (AlEt(2)) and base (PPh(2)) 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.