金属卟啉/碳纳米管仿生催化剂的制备及其在Baeyer-Villiger氧化反应中的催化机理

Preparation of metalloporphyrin/carbon nanotube biomimetic catalysts and its catalytic mechanism in baeyer-villiger oxidation

利用金属卟啉环(TPP)上π电子与多壁碳纳米管(MWCNTs)上π电子之间的π-π堆积效应,成功制备了4种金属卟啉/多壁碳纳米管催化剂(FeTPPCl-π-π-c-MWCNTs、FeTPPCl-π-π-MWCNTs、SnTPP-π-π-cMWCNTs和SnTPP-π-π-MWCNTs)。实验表明,所制备产物可用于酮类化合物Baeyer-Villiger(B-V)氧化反应的仿生催化剂。当反应温度为50℃,1,2-二氯乙烷为溶剂,FeTPPCl-π-π-c-MWCNTs为催化剂,环己酮的转化率达到96%,ε-己内酯的收率为96%。另外,所制备的催化剂对于其他酮类化合物的B-V氧化也表现出良好的催化活性。进一步通过原位电子顺磁共振波谱和原位紫外光谱研究了环己酮的B-V氧化的反应历程,发现金属卟啉/碳纳米管仿生催化剂能同时提高自由基和金属卟啉高价活性物种的稳定性,这有利于增强金属卟啉仿生催化酮类化合物的活性。

Four kinds of metalloporphyrin/multi-walled carbon nanotube catalysts(Fe TPPCl-π-π-cMWCNTs,Fe TPPCl-π-π-MWCNTs,Sn TPP-π-π-c-MWCNTs and Sn TPP-π-π-MWCNTs) were successfully prepared by utilizing the π-π stacking effect between the π electrons on the metalloporphyrin ring and on the wall of the multi-walled carbon nanotube.The experiments showed that the prepared products can be used as biomimetic catalyst for the Baeyer-Villiger(B-V) oxidation of ketones.The conversion of cyclohexanone to ε-caprolactone could reach 96%,and the yield of ε-caprolactone was 96%with FeTPPCl-π-π-c-MWCNTs as catalyst and 1,2-dichloroethane as solvent at 50℃ under the optimized conditions.In addition,the as-prepared catalysts also showed good catalytic activity for the B-V oxidation of other ketones.The process of B-V oxidation of cyclohexanone was further systematically studied by in situ electron paramagnetic resonance spectroscopy and in situ ultraviolet spectroscopy.It is found that the metalloporphyrin/carbon nanotube biomimetic catalysts can simultaneously improve the stability of free radicals and metalloporphyrin high-valent active species,which is beneficial to enhance the biomimetic activity of metalloporphyrin in the B-V oxidation of ketone compounds.