有机-无机杂化钙钛矿基光催化剂用于可见光催化芳香族溴化反应并联产氢气

doi:10.1016/S1872-2067(22)64101-9

摘要/Abstract

摘要：

溴化反应是一类很重要的有机反应. 有机溴化物广泛存在于自然界, 并广泛应用于医药、农药、染料、香料阻燃剂等化工行业, 其在药物合成中有着尤其重要的意义. 有机溴化物还被广泛用于形成碳‒碳键和碳‒杂键的有机反应, 如Suzuki-Miyaura, Sonogashira, Heck, Stille和Buchwald-Hartwig等交叉偶联反应. 传统的有机溴化物合成方法不符合绿色合成的要求, 存在原子经济性低、不环保等问题. 作为一种高效、绿色、有前景的有机合成手段, 光催化已成功用于各种有机反应, 如氧化反应、还原反应以及C‒X (C, O, N, S)键的形成. 与具有毒性、腐蚀性和危险性的分子溴(Br₂)和昂贵的N-溴代琥珀酰亚胺(NBS)相比, 无毒且价格低廉的溴化氢(HBr)可作为相对理想的“绿色”溴源参与溴化反应. 需要说明的是, HBr中的Br^‒必须被活化为活性物质才能参与溴化反应. 本工作选择HBr为溴源, 创建了一个以有机-无机杂化钙钛矿材料为光催化剂的光催化溴化体系, 在可见光照射下, 反应可获得高价值的芳香溴化物, 并同时获得氢气.

本课题组前期工作(ACS Energy Lett., 2019, 4, 40-47)发现, 可见光吸收性能强的有机-无机杂化钙钛矿甲基胺溴化铅(MAPbBr₃)可以在HBr中稳定存在, 并在可见光照射下分解HBr产生H₂. 本文以MAPbBr₃为光催化剂, HBr为溴源, 完成了芳香化合物的溴化反应, 同时保留了产生H₂的优势. 在MAPbBr₃饱和的HBr水溶液中, MAPbBr₃的沉淀物及在HBr饱和溶液中的溶解物之间形成了溶解-析出动态平衡, MAPbBr₃处于稳定状态. 助催化剂0.75 wt%Pt/Ta₂O₅和导电聚合物聚3,4-乙烯二氧噻吩/聚苯乙烯磺酸盐(PEDOT:PSS)分别作为电子和空穴传输通道存在, 有效促进了光生电子和空穴的分离, 增强了光催化反应的活性. N,N-二甲基甲酰胺(DMF)有效提高了有机底物在反应体系中的溶解性, 而且不会破坏体系的稳定性, 可以进一步提升反应的活性. 与DMF结构类似的有机物同样可以提高反应活性, 其中N,N-二异丁基甲酰胺效果最好. 机理研究表明, 此溴化反应是通过亲电取代的方式进行的, 反应生成的Br₂会与水反应生成活性溴化物种HOBr, HOBr可能是关键的溴化中间体. 这种温和且高效的溴化路径, 反应的转化率和选择性均高达99%, 可以完成芳香有机物的溴化, 还可以用于结构复杂的天然物质和药物的后期功能化.

关键词: 光催化, 溴化反应, 氢气, 有机-无机杂化钙钛矿材料, 甲基胺溴化铅

Abstract:

Aromatic bromides are important chemicals in nature and chemical industries. However, their traditional synthesis routes suffer from low atomic economy and pollutant formation. Herein, we show that organic-inorganic hybrid perovskite methylammonium lead bromide (MAPbBr₃) nanocrystals stabilized in aqueous HBr solution can achieve simultaneous aromatic bromination and hydrogen evolution using HBr as the bromine source under visible light irradiation. By hybridizing MAPbBr₃ with Pt/Ta₂O₅ and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate as electron- and hole-transporting motifs, aromatic bromides were achieved from aromatic compounds with high yield (up to 99%) and selectivity (up to 99%) with the addition of N,N-dimethylformamide or its analogs. The mechanistic studies revealed that the bromination proceeds via an electrophilic attack pathway and that HOBr may be the key intermediate in the bromination reaction.

Key words: Photocatalysis, Bromination, Hydrogen, Organic-inorganic hybrid perovskite material, Methylammonium lead bromide

张艳飞, 王洪, 刘䶮, 李灿. 有机-无机杂化钙钛矿基光催化剂用于可见光催化芳香族溴化反应并联产氢气[J]. 催化学报, 2022, 43(7): 1805-1811.

Yanfei Zhang, Hong Wang, Yan Liu, Can Li. Aromatic bromination with hydrogen production on organic-inorganic hybrid perovskite-based photocatalysts under visible light irradiation[J]. Chinese Journal of Catalysis, 2022, 43(7): 1805-1811.

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链接本文: https://www.cjcatal.com/CN/10.1016/S1872-2067(22)64101-9

https://www.cjcatal.com/CN/Y2022/V43/I7/1805

图/表 7

Fig. 1. XRD pattern (a) and UV-vis diffuse reflectance spectrum (b) of the as-synthesized MAPbBr3 powder.

Fig. 2. Photocatalytic bromination performance over several catalysts. Reaction conditions: MAPbBr3 (150 mg), Pt (0.75 wt%)/Ta2O5 (7.5 mg), PEDOT:PSS (200 μL), saturated aqueous HBr solution (5 mL), substrate (0.05 mmol), 300-W Xe lamp (λ > 420 nm, 160 mW cm-2), Ar atmosphere, room temperature, 6 h. Conversion and selectivity were determined using crude proton nuclear magnetic resonance (1H NMR) spectroscopy. The amount of H2 was determined using a gas chromatograph.

Fig. 3. (a) Effect of organic solvents on the photocatalytic reaction. (b) Effect of the amount of DMF on the photocatalytic reaction. (c) Effect of the DMF analogs S on the photocatalytic reaction. Reaction conditions: MAPbBr3 (150 mg), Pt (0.75 wt%)/Ta2O5 (7.5 mg), PEDOT:PSS (200 μL), saturated aqueous HBr solution (5 mL), substrate (0.05 mmol), organic solvent, 300-W Xe lamp (λ > 420 nm, 160 mW cm-2), Ar atmosphere, room temperature, 6 h. Conversion and selectivity were determined using crude 1H NMR spectroscopy. The amount of H2 was determined using a gas chromatograph.

Table 1 Photocatalytic bromination of aromatic compounds a.

Entry	Time (h)	Conversion ^b (%)	Selectivity ^b (%)	[H₂] ^c (%)
1	6	>99	>99	>99
2	12	86	>99	76
3	16	>99	>99	>99
4	12	>99	>99	77
5	18	>99	>99	>99
6	6	>99	>99	80
7	6	>99	>99	89
8	12	>99	>99	97
9	19	>99	>99	>99
10	6	>99	>99	94
11	36	>99	>99	80
12	23	>99	>99	91
13	12	>99	>99	>99
14	12	45	>99	>99
15	12	>99	>99	80
16	12	>99	>99	>99
17	24	>99	>99	90

Table 2 Direct photocatalytic bromination of the natural product, drug and intermediate of materials.

Entry	Time (h)	Conversion^b(%)	Selectivity^b(%)	[H₂]^c(%)
1	48	73	>99	>99
2	72	72	>99	>99
3	24	>99	>99	>99

Fig. 4. Mechanistic studies. (a) UV-Vis spectra of the solutions for photocatalytic reactions (before reaction, under light, and under light with H3PO2) and 3% bromine water. (b) The Hammett equation of the substituted anisole. Reaction conditions for figure (b): MAPbBr3 (150 mg), Pt(0.75 wt%)/Ta2O5 (7.5 mg), PEDOT:PSS (200 μL), saturated aqueous HBr solution (5 mL), substrate (0.05 mmol), DBF (0.05 mmol), 300-W Xe lamp (λ > 420 nm, 160 mW cm-2), Ar atmosphere, room temperature, 6 h.

Fig. 5. Schematic illustration of the reaction mechanism.

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