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

The N-geminal P/Al Lewis pair [Ph 2 PN(2,6- i Pr 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- i Pr 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- i Pr 2 C 6 H 3 )AlEt 2 ](CPh= ⌝ CEt) ( 4a ) and [Ph 2 ⌜ PN(2,6- i Pr 2 C 6 H 3 )AlEt 2 ](CEt= ⌝ CPh) ( 4b ); and with other alkynes generated [Ph 2 ⌜ PN(2,6- i Pr 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.