By combining bases that are known to racemize benzylic amines with a nickel(II) salt, active nickel nanoparticles were obtained that can be used as catalysts in the racemization of both aliphatic and benzylic primary amines. The nanoparticles are stable in the ionic liquid tetrabutylammonium bromide and can complete most racemizations within a few hours with excellent selectivity. The problem of the incompatibility of the strongly reducing racemization catalyst and the enzymatic amine resolution catalyst was overcome by using a two‐pot system with a biphasic racemization step. Consecutive contact of a nonane layer that contained the amine with the acylating enzyme and with the racemizing Ni nanoparticles in the ionic liquid allowed the 50 % amide yield limit of a kinetic resolution to be successfully surpassed.
The different mechanisms by which the support and the solvent can influence the catalytic properties of a metal nanoparticle (NP) are reviewed. The use of a support not only significantly facilitates the recycling of NPs but also has many additional advantages varying from enhanced stabilization of the NP dispersion to the alteration of the electronic properties of the metal, shape selectivity effects, and even active participation in the reaction mechanism. The correct choice of solvent, on the other hand, can drastically influence properties such as the morphology of the particles and, in the case of alloys, determine the composition of the NPs. Judicious solvent selection also enhances recyclability and stability, and in some cases, the solvent plays a cocatalytic role. Despite the many beneficial effects of combining metal NPs with the correct support or solvent, many processes are not well understood. Further research should be conducted on elucidating the general mechanisms behind the support-NP or solvent-NP interactions.
It doesn′t cost a dime: A nickel‐based system that catalyzes the aromatic amination of aryl chlorides is presented. Starting from a simple Ni(II) salt, aliphatic phosphonium‐based ionic liquids (ILs) were found to stabilize the nickel nanoparticles formed in situ during the reaction. The IL also enables successful recycling of the system after the reaction.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.