Study on Synthesis and H2-Liberation Reaction of the Frustrated Lewis Pair (FLP)-Type Aluminum Hydrides

doi:10.6023/cjoc202510011

Chinese Journal of Organic Chemistry ›› 2026, Vol. 46 ›› Issue (3): 881-887.DOI: 10.6023/cjoc202510011 Previous Articles Next Articles

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受阻Lewis酸碱对(FLP)型铝氢化合物的合成及其放H₂反应研究

陈艺林^a^,^b^,^*(), 朱成建^a^,^*()

^a 南京大学化学化工学院南京 210023
^b 江苏南大光电材料股份有限公司江苏苏州 215000

收稿日期:2025-10-16 修回日期:2025-11-24 发布日期:2026-01-15
通讯作者: 陈艺林, 朱成建
基金资助:
国家自然科学基金(22271144)

Study on Synthesis and H₂-Liberation Reaction of the Frustrated Lewis Pair (FLP)-Type Aluminum Hydrides

Yilin Chen^a^,^b^,^*(), Chengjian Zhu^a^,^*()

^a School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023
^b Jiangsu Nata Opto-electronic Material Co., Ltd., Soochow, Jiangsu 215000

Received:2025-10-16 Revised:2025-11-24 Published:2026-01-15
Contact: Yilin Chen, Chengjian Zhu
Supported by:
National Natural Science Foundation of China(22271144)

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Abstract

Synthesis and H₂-liberation properties of N/Al frustrated Lewis pair (FLP)-type aluminum hydrides have been studied. By use of 2,2,6,6-tetramethylpiperidine, iodobenzene, n-BuLi, AlCl₃, and LiAlH₄ as precursor materials for the five-step organometallic synthesis route, FLP aluminum dihydride (o-TMP-C₆H₄)AlH₂ [1, TMP= N(CMe₂CH₂)₂CH₂] that featured an intremolecular N→Al bonding was prepared. Compound 1 was occurred by a disproportionational H₂-liberation in toluene at 80 ℃ to give aluminum monohydride (o-TMP-C₆H₄)₂AlH (2), while compound 2 was able to react by further H₂- liberation at 50 ℃ via dehydrogenation of 3-C(sp²)—H of N-methylindole, affording [(o-TMP-C₆H₄)]₂Al(3-C₈H₅NMe) (3). Compound 1 reacted readily with indole at －30 ℃ to afford H₂-releasing compound [(o-TMP-C₆H₄)Al(μ-H)(NC₈H₆)]₂ (4). Compound 4 further reacted with indole at room temperature to generate (o-TMP-C₆H₄)Al(NC₈H₆)₂ (5). Finally, compound 1 reacted with B(C₆F₅)₃ by a group exchange between Al—H and B—C₆F₅ bonds to afford (o-TMP-C₆H₄)(C₆F₅)Al(μ-H)₂- B(C₆F₅)₂ (6), which features an Al(μ-H)₂B 3c-2e bond. Upon treatment with Al(C₆F₅)₃, metathesis between Al—H and Al—C₆F₅ bonds occurred to give [(o-TMP-C₆H₄)(C₆F₅)Al(μ-H)]₂ (7) containing an Al(μ-H)₂Al 3c-2e bond. Compounds 1~7 all exhibit N/Al FLP-character. The H₂-liberation reactions of 1, 2 and 4 were assisted by the concerted activation of either the C(sp²)—H or N—H bonds via the N/Al FLP moieties.

Key words: N/Al FLP-type aluminum hydride, H₂-liberation reaction, FLP-type activation, 3c-2e bond compound

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Yilin Chen, Chengjian Zhu. Study on Synthesis and H₂-Liberation Reaction of the Frustrated Lewis Pair (FLP)-Type Aluminum Hydrides[J]. Chinese Journal of Organic Chemistry, 2026, 46(3): 881-887.

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Fig. & Tab. 11

Scheme 1. Synthetic route to (o-TMP-C6H4)I

Scheme 2. Synthetic route to N/Al FLP compound 1

Scheme 3. H2-Liberation reaction by solvent thermal treatment of compound 1 for synthesis of compound 2

Figure 1. X-ray crystal structures of compounds 2 (left) and 3 (right) with thermal ellipsoids at 50% probability

Figure 2. Result for the 1H NMR spectrium-traced reaction (a) 1H NMR spectrium of 1 in CDCl3; (b) 1H NMR spectrium-traced heat treatment of 1 in CDCl3; (c) 1H NMR spectrium of 2 in CDCl3

Scheme 4. H2-Liberation reaction by dehydrogenation of the C(sp2)—H of N-methylindole of compound 2 and the related FLP-type activation mechanism

Compd.	Al—C	Al—N	C—Al—N	Al—H
1^a	0.1944(1)	0.2311(1)	66.90(1)	0.1478(18) 0.1585(16)
2	0.1990(7) 0.1990(7)	0.2416(6) 0.2461(6)	64.30(2) 64.70(2)	0.1520(4)
3	0.1959(4) 0.1987(3)	0.2678(3) 0.3129	51.70 60.0(6)
4	0.1937(2)	0.2233(2)	68.70(9)	0.1520(2) 0.1967(2)
6	0.1918(3)	0.2133(2)	71.25(8)	0.1740(2) 0.1868(18)
7	0.1940(2)	0.2288(2)	67.59(7)	0.1596(2) 0.1940(18)

Table 1. Bond lengths (nm) and angles (°) for (o-TMP-C6H4)Al and AlH moieties of the FLP compounds 1~4 and 6, 7

Scheme 5. H2-Liberation reaction by dehydrogenation of the NH of indole using compound 1 and the related FLP-type concerted activation mechanism

Figure 3. X-ray crystal structure of compounds 4 with thermal ellipsoids at 50% probability

Scheme 6. Reactions of compound 1 with the respective B(C6F5)3 and Al(C6F5)3 for synthesis of compounds 6 and 7

Figure 4. X-ray crystal structures of 6 (left) and 7 (right) with both thermal ellipsoids at 50% probability level

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受阻Lewis酸碱对(FLP)型铝氢化合物的合成及其放H₂反应研究

Study on Synthesis and H₂-Liberation Reaction of the Frustrated Lewis Pair (FLP)-Type Aluminum Hydrides

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受阻Lewis酸碱对(FLP)型铝氢化合物的合成及其放H2反应研究