凹凸棒土固载N-杂环卡宾催化安息香缩合反应

Attapulgite supported NHCs as recyclable and efficient catalysts for benzoin reactions

摘要:

本文将五种不同的NHCs催化剂前体接枝到凹凸棒土表面，制备了五种负载型NHCs催化剂。通过FT-IR、元素分析、BET和SEM对五种催化剂进行了表征，表征结果表明NHCs催化剂前体成功地固定在凹凸棒土表面。进一步的实验结果表明，这些负载型NHC可以作为安息香反应的有效催化剂。接着探究了这些负载型催化剂催化安息香反应的优化条件。结果发现，当BTBCl@ATP(催化剂B, 1 mmol%咪唑盐)作为催化剂，0.4当量NaOH作为碱，2ml CH3OH作为溶剂，在110℃油浴中，在Ar气氛中反应8小时，收率最高。在此优化条件下，负载型NHCs催化剂可以催化多种芳香醛的安息香反应，产率为61-86%。催化剂的重复使用实验表明，这些负载型催化剂可以简单地从反应体系中分离出来，重复使用四次后，这些负载型催化剂的催化活性没有明显下降。

Abstract:

In this paper, five different NHCs catalyst precursors were grafted onto the surface of attapulgite to form five supported NHCs catalysts. The five catalysts were characterized by FT-IR, elemental analysis, BET and SEM, and characterization results showed that NHCs catalyst precursors were successfully immobilized on the surface of the attapulgite. Further experimental results showed that these supported NHCs can be used as efficient catalysts for benzoin condensations. Then, the optimal conditions of the benzoin condensation catalyzed by these supported catalysts were explored. It was discovered that the optimized conditions employed BTBCl@ATP (Catalyst B, 1 mmol% imidazolium salt) as catalyst, 0.4 equiv. NaOH as base and 2ml CH3OH as solvents at 110oC in Ar atmosphere. Under this optimized condition, the supported NHCs catalyst could catalyze benzoin reactions of various aromatic aldehydes with 61-86% yields. The reuse experiment of the catalyst showed that these supported catalysts can be simply separated from the reaction system, and the catalytic activity of these supported catalysts does not decline significantly after reuse for four times.