Unprecedented NH2-MIL-101(Al)/n-Bu4NBr system as solvent-free heterogeneous catalyst for efficient synthesis of cyclic carbonates via CO2 cycloaddition†,Dalton Transactions

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Unprecedented NH2-MIL-101(Al)/n-Bu4NBr system as solvent-free heterogeneous catalyst for efficient synthesis of cyclic carbonates via CO2 cycloaddition†
Dalton Transactions ( IF 3.5 ) Pub Date : 2017-11-28 00:00:00 , DOI: 10.1039/c7dt03754f
S. Senthilkumar _{1,

2,

3,

4} , Minaxi S. Maru _{1,

2,

3,

4} , R. S. Somani _{1,

2,

3,

4} , H. C. Bajaj _{1,

2,

3,

4} , Subhadip Neogi _{1,

2,

3,

4}

Affiliation

Amine-functionalised framework NH₂-MIL-101(Al) was synthesized using a solvothermal and microwave method and characterized by PXRD, FT-IR, TGA, SEM-EDX, and BET surface area analysis. The desolvated framework, in the presence of co-catalyst tetrabutylammonium bromide (TBAB), acted as an excellent heterogeneous catalyst for the solvent-free cycloaddition of carbon dioxide (CO₂) with epoxides, affording five-membered cyclic carbonates. Using styrene oxide, the NH₂-MIL-101(Al)/TBAB system showed more than 99% conversion, affording 96% yield and 99% selectivity with a turn over frequency of 23.5 h⁻¹. This validated the synergistic effect of the quaternary ammonium salt during CO₂ cycloaddition. The catalyst could be recycled at least five times without a noticeable loss in activity, while leaching test showed no leached Al³⁺ ions throughout the reaction. Thorough analysis of the reaction parameters showed that the optimum conditions for obtaining the maximum yield and highest selectivity were 120 °C and 18 bar of CO₂ for 6 h. The outstanding conversion and selectivity were maintained for a range of aliphatic and aromatic epoxides, corroborating the duel benefit of the micro–mesoporous system with amine functionality, which offered easy access for reactant molecules with diverse sizes, and provided inspiration for future CO₂ cycloaddition catalytic systems. We also propose a rationalized mechanism for the cycloaddition reaction mediated by NH₂-MIL-101(Al) and TBAB based on literature precedent and experimental outcome.

中文翻译：

前所未有的NH ₂ -MIL-101（Al）/ n -Bu ₄ NBr系统作为无溶剂多相催化剂，可通过CO ₂环加成有效合成环状碳酸酯†

使用溶剂热和微波方法合成了胺官能化的骨架NH ₂ -MIL-101（Al），并通过PXRD，FT-IR，TGA，SEM-EDX和BET表面积分析对其进行了表征。的去溶剂化的框架，在助催化剂四丁基溴化铵（TBAB）的存在下，充当了二氧化碳的无溶剂环加成优异的非均相催化剂（CO ₂与环氧化物），得到五元环环状碳酸酯。使用氧化苯乙烯，NH ₂ -MIL-101（Al）/ TBAB系统显示出超过99％的转化率，提供96％的收率和99％的选择性，转换频率为23.5 h ^-1。这证实了季铵盐在CO ₂期间的协同作用。环加成。催化剂可以循环至少五次而没有明显的活性损失，而浸出试验表明在整个反应过程中没有浸出的Al ³⁺离子。对反应参数的透彻分析表明，获得最大收率和最高选择性的最佳条件是120°C和18 bar CO ₂持续6 h。各种脂族和芳族环氧化物均保持了出色的转化率和选择性，从而证实了具有胺功能的微介孔体系的双重优势，可轻松获得各种尺寸的反应物分子，并为未来的CO ₂提供了灵感环加成催化系统。我们还基于文献的先例和实验结果，提出了一种由NH ₂ -MIL-101（Al）和TBAB介导的环加成反应的合理机制。

更新日期：2017-11-28

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