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. 2017 Jun 1;2(6):2405-2414.
doi: 10.1021/acsomega.7b00236. eCollection 2017 Jun 30.

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

Shuang Ding  1 , Jiancheng Li  1 , Rui Liu  1 , Gang Fu  1 , Hongping Zhu  1 , Weiping Liu  2 , Qingsong Ye  2
Affiliations

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

Shuang Ding et al. ACS Omega. .

Abstract

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 [Ph2 ⌜PN(2,6-iPr2C6H3)AlEt2](CR=⌝CR) (R = Me (2), Ph (3)); with PhC≡CEt produced two isomers, [Ph2 ⌜PN(2,6-iPr2C6H3)AlEt2](CPh=⌝CEt) (4a) and [Ph2 ⌜PN(2,6-iPr2C6H3)AlEt2](CEt=⌝CPh) (4b); and with other alkynes generated [Ph2 ⌜PN(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.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Scheme 1
Scheme 1. Reported Zwitterionic Heterocycloalkenes Formed by (F)LP–alkyne Cycloadditions
Scheme 2
Scheme 2. Synthesis of N-Geminal P/Al LP
Figure 1
Figure 1
X-ray crystal structure of 1. The carbon atoms of the aryl groups at both the P and N atoms are drawn with thermal ellipsoids at a 10% probability level for clarity and the other atoms, at a 50% probability level. Selected bond lengths (Å) and angles (°): N(1)–P(1), 1.674(2); P(1)–Al(2), 2.545(1); Al(2)–N(2), 1.903(2); N(2)–P(2), 1.670(2); P(2)–Al(1), 2.563(1); Al(1)–N(1), 1.893(2); P(1)–N(1)–Al(1), 122.87(11); P(2)–N(2)–Al(2), 122.09(11); N(1)–Al(1)–P(2), 106.19(7); N(2)–Al(2)–P(1), 106.47(7).
Scheme 3
Scheme 3. Dipolar Cycloaddition Reactions of 1 with Internal Alkynes to Zwitterionic C2PNAl-Heterocyclopentenes 2–7
Scheme 4
Scheme 4. Dipolar Cycloaddition Reactions of 1 with Terminal Alkynes To Form Zwitterionic C2PNAl-Heterocyclopentenes 8 and 9
Figure 2
Figure 2
X-ray crystal structure of 2 with thermal ellipsoids at a 50% probability level. Selected bond lengths (Å) and angles (°): P(1)–N(1), 1.626(2); N(1)–Al(1), 1.956(2); Al(1)–C(2), 2.007(2); C(2)–C(3), 1.345(3); C(3)–P(1), 1.786(2); Al(1)–N(1)–P(1), 112.23(8); N(1)–P(1)–C(3), 106.28(8); P(1)–C(3)–C(2), 114.16(14); C(3)–C(2)–Al(1), 116.61(14); C(2)–Al(1)–N(1), 90.46(7).
Figure 3
Figure 3
X-ray crystal structure of 4a with thermal ellipsoids at a 50% probability level. Selected bond lengths (Å) and angles (°): N(1)–P(1), 1.623(1); P(1)–C(2), 1.788(2); C(2)–C(1), 1.349(2); C(1)–Al(1), 2.024(2); Al(1)–N(1), 1.960(1); Al(1)–N(1)–P(1), 111.69(7); N(1)–P(1)–C(2), 106.23(7); P(1)–C(2)–C(1), 113.64(12); C(2)–C(1)–Al(1), 116.38(12); C(1)–Al(1)–N(1), 89.85(6).
Figure 4
Figure 4
X-ray crystal structure of 6 with thermal ellipsoids at a 50% probability level. Selected bond lengths (Å) and angles (°): N(1)–P(1), 1.623(2); P(1)–C(2), 1.819(2); C(2)–C(1), 1.350(3); C(1)–Al(1), 2.017(2); N(1)–Al(1), 1.952(2); Al(1)–N(1)–P(1), 112.48(8); N(1)–P(1)–C(2), 104.59(8); P(1)–C(2)–C(1), 114.67(13); C(2)–C(1)–Al(1), 115.31(13); C(1)–Al(1)–N(1), 90.78(7).
Figure 5
Figure 5
X-ray crystal structure of 8 with thermal ellipsoids at a 50% probability level. Selected bond lengths (Å) and angles (°) (the value in brackets is for another independent molecule): N(1)–P(1), 1.619(2) [1.622(2)]; P(1)–C(1), 1.783(2) [1.781(2)]; C(1)–C(2), 1.348(3) [1.343(3)]; C(2)–Al(1), 2.018(2) [2.019(3)]; Al(1)–N(1), 1.959(2) [1.966(2)]; P(1)–N(1)–Al(1), 112.54(10) [112.02(10)]; N(1)–P(1)–C(1), 104.03(10) [104.23(10)]; C(2)–C(1)–P(1), 117.47(18) [117.60(18)]; C(1)–C(2)–Al(1), 113.25(16) [113.36(16)]; N(1)–Al(1)–C(2), 90.94(9) [90.85(9)].
Scheme 5
Scheme 5. Dipolar Cycloaddition Reactions of 1 with an Alkene, Nitrile, and Carbodiimide To Form Zwitteric Heterocycles 10–12
Figure 6
Figure 6
X-ray crystal structure of 10 with thermal ellipsoids at a 50% probability level. Selected bond lengths (Å) and angles (°): P(1)–N(1), 1.624(2); P(1)–C(2), 1.834(2); C(2)–C(1), 1.551(3); C(1)–Al(1), 2.019(2); Al(1)–N(1), 1.972(2); Al(1)–N(1)–P(1), 112.61(9); N(1)–P(1)–C(2), 103.97(8); P(1)–C(2)–C(1), 106.19(13); C(2)–C(1)–Al(1), 108.25(12); C(1)–Al(1)–N(1), 91.86(7).
Figure 7
Figure 7
X-ray crystal structure of 11 with thermal ellipsoids at a 50% probability level. Selected bond lengths (Å) and angles (°): N(2)–P(1), 1.625(2); P(1)–C(1), 1.891(3); C(1)–N(1), 1.244(4); N(1)–Al(1), 1.905(2); Al(1)–N(2), 1.944(2); Al(1)–N(2)–P(1), 113.19(12); N(2)–P(1)–C(1), 100.04(11); P(1)–C(1)–N(1), 115.0(2); C(1)–N(1)–Al(1), 119.62(18); N(1)–Al(1)–N(2), 91.04(9).
Figure 8
Figure 8
X-ray crystal structure of 12 with thermal ellipsoids at a 50% probability level. Selected bond lengths (Å) and angles (°): N(3)–P(1), 1.623(2); P(1)–C(1), 1.862(2); C(1)–N(1), 1.369(2); N(1)–Al(1), 1.895(2); Al(1)–N(3), 1.941(2); C(1)–N(2), 1.279(3); Al(1)–N(3)–P(1), 112.65(9); N(3)–P(1)–C(1), 104.30(8); P(1)–C(1)–N(1), 108.99(14); C(1)–N(1)–Al(1), 121.54(12); N(1)–Al(1)–N(3), 90.65(7).
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