Palladium-guanidine complex immobilized on SBA-16: a highly active and recyclable catalyst for Suzuki coupling and alcohol oxidation
作者:Hengquan Yang、Xiaojing Han、Zhancheng Ma、Runqin Wang、Jing Liu、Xiangfei Ji
DOI:10.1039/b919175e
日期:——
By immobilizing a mixture of a palladium-guanidine complex and guanidine on the mesoporous cage-like material SBA-16 via a one-pot silylation, we have successfully prepared a new solid catalyst for Suzuki coupling and the aerobic oxidation of alcohols. The structure and composition of the solid catalyst were characterized with N2 sorption, XRD, TEM, FT-IR and solid state NMR. The coordination state of the palladium-guanidine complex supported on the solid catalyst was preliminarily investigated with XPS and UV-vis spectroscopy. This catalyst afforded fast conversions for the Suzuki coupling of various aryl bromides and arylboronic acids in a 50% aqueous ethanol solution at 50 °C even at loadings of 0.01–0.001 mol%, and the TOF (turn-over frequency) for the Suzuki coupling of bromobenzene and arylboronic acids could be up to 45 700 h−1 under mild conditions. A satisfactory yield was obtained even after the catalyst was reused several times. The developed solid catalyst combined with the mild conditions investigated represents one of the most efficient heterogeneous systems for the Suzuki coupling of bromides. Furthermore, it was found that the solid catalyst could also work well for the aerobic oxidation of benzylic alcohols and cinnamyl alcohol, affording over 99% selectivity. The catalyst could be reused 15 times without a significant decrease in activity and selectivity.
通过对一种含有钯-胍复合物和胍的混合物进行一次性硅化,并将其固定在介孔笼状材料SBA-16上,我们成功制备了一种用于铃木偶联反应和醇的有氧氧化的新型固体催化剂。该固体催化剂的结构和成分通过氮气吸附、XRD、透射电镜(TEM)、傅里叶变换红外光谱(FT-IR)和固态核磁共振(NMR)进行了表征。使用XPS和紫外-可见光谱对固体催化剂上支持的钯-胍复合物的配位状态进行了初步研究。该催化剂在50°C的50%水乙醇溶液中,对于多种芳基溴化物和芳基硼酸的铃木偶联反应展现出快速的转化率,即使在0.01-0.001 mol%的负载下,溴苯和芳基硼酸的铃木偶联反应的TOF(转换频率)可以高达45,700 h−1,且在温和条件下也能获得满意的产率,即使催化剂被重复使用多次。所开发的固体催化剂结合所研究的温和条件,代表了铃木偶联反应中最有效的异相催化体系之一。此外,还发现该固体催化剂同样适用于苄醇和肉桂醇的有氧氧化,选择性超过99%。该催化剂可重复使用15次而活性和选择性并未显著下降。