Development of recyclable gold nanoparticles for routine benchtop catalysis in organic transformations.

hydration;hydroamination;hydrochlorination;semi-reduction;reductive amination;recyclable

Shengzong Liang

University:University of Louisville

Department:Chemistry

关键词: hydration;    hydroamination;    hydrochlorination;    semi-reduction;    reductive amination;    recyclable;   

Others  :  https://ir.library.louisville.edu/cgi/viewcontent.cgi?article=3734&context=etd

美国|英语

来源: The Universite of Louisville's Institutional Repository

【 摘 要 】

Homogeneous gold catalysis is a popular research area due to its high efficiency. Various gold catalysts have been utilized in organic synthesis and their reaction mechanisms are also well understood. However, most gold catalysis suffers from high catalyst loading or catalyst decay problems. In addition, homogeneous gold catalysts are not recyclable. These disadvantages have limited their application in large-scale synthesis and also caused a serious waste of this precious metal. A solution for these problems is to use a recyclable heterogeneous gold catalyst. So in this study, with the aim of making gold chemistry greener we successfully used heterogeneous gold nanoparticles (Au/TiO2) as catalyst on several types of organic transformations where they functioned as a “Swiss army knife” multipurpose heterogeneous catalyst. On the one hand, similarly as homogeneous gold catalysis, small amount of cationic gold species on Au/TiO2 could act as soft Lewis acid for the activation of C-C unsaturated bonds especially triple bond, promoting the facile nucleophilic addition of various nucleophiles. For example, the nucleophilic attack of catalytical amount of morpholine followed by hydration of the resulting imine intermediate could lead to an overall efficient alkyne hydration catalyzed by Au/TiO2 under basic conditions. This methodcould tolerate substrates bearing highly acid-sensitive functional groups like silyl ethers or ketals that usually can’t survive in conventional acidic alkyne hydration systems. In addition, amines could also serve as nucleophile to furnish corresponding amine products after reduction which is derived from alkyne hydroamination reaction. Moreover, a novel chlorinating reagent HCl/DMPU was designed by our group, in the presence of Au/TiO2, it could deliver chlorine onto alkynes to give vinylchlorides in good regioselectivity. On the other hand, the main component of gold nanoparticles: gold(0) species could efficiently dissociate transfer hydrogen reagents such as ammonium formate and formic acid, thus the resulting gold hydride species could easily mediate the highly stereoselective semireduction of alkynes and reductive amination of carbonyl compounds respectively. It is noteworthy that the gold nanoparticles could be recycled easily without significant loss of activity in most of cases.