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Sputtering-deposition of metallic nanoparticles onto chiral ionic liquids andapplications in enantioselective hydrogenation

Periodic Reporting for period 1 - SDchirnanocat (Sputtering-deposition of metallic nanoparticles onto chiral ionic liquids andapplications in enantioselective hydrogenation)

Reporting period: 2016-08-01 to 2018-07-31

The production of fine chemicals, such as chiral molecules, is one of the main applications of the chemical industry. However, any new process developed in Europe should be environmentally sound. Specifically, metallic nanoparticles (MNPs) are employed as catalysts for the production of compounds with interest in different fields, with the great advantage of being easily recyclable and reusable. These species can be generated and immobilized in ionic liquids (ILs), salts with melting point below 100 ºC, allowing the straightforward separation of products and recycling of the system. In addition, ILs are not “innocent” media and have a relevant influence in these transformations. The use of ILs with asymmetric properties can induce the formation of a specific enantiomer of each product. SDchirnanocat project focuses on the formation of chiral products by the use of enantioselective catalytic systems obtained merging the asymmetric properties of newly synthesized ILs with the catalytic activity of MNPs. To this end, MNPs were prepared onto ILs by sputtering-deposition (SD), an innovative technique which enables the fast synthesis of clean MNPs, avoiding the use of organic solvents and reducing agents. In contrast to other physical techniques, the SD of MNPs onto ILs allows the control of the size and shape of MNPs by the appropriate tuning of the sputtering conditions. These three concepts (MNP, chiral IL and SD) converge into the main aim of this project: The development of a novel enantioselective catalytic system based on MNPs prepared by SD onto chiral ILs for asymmetric hydrogenation reactions (Figure 1). Thus, SDchirnanocat addresses one major issue for society: the development of new methodologies for the preparation of high-value and fine chemicals in an environmental friendly way.
The overall objectives of SDchirnanocat are: (1) the design and synthesis of “new” chiral imidazolium based ILs with different substituents whose ion pairs would act as chiral inductors; (2) generation of MNPs by SD onto chiral ILs; (3) application of the new optimized chiral MNP-IL system(s) in asymmetric hydrogenation.
The first Work Package (WP1) focuses on the synthesis of new chiral imidazolium based ILs. 6 chiral imidazolium halide salts were obtained by reaction of 2 imidazolium backbones with 3 different chiral branches (Figure 2). Next, the anion exchange reaction with imidazole and natural chiral amino acids (L-leucine and L-phenylalanine) led to the synthesis of the new chiral ILs (Figure 3), which were fully characterized. In parallel, we prepared a new family of benzimidazolium-based chiral ILs from natural secondary alcohols (Figure 4), which were used as chiral recognition agents. This research work was published in Physical Chemistry Chemical Physics (Phys. Chem. Chem. Phys 2018, 20, 20821; gold open access under process).
The second Work Package (WP2) consists in the SD of MNPs on chiral imidazolium based ILs. Nearly all ILs showed very high viscosity and led to the formation of a metal mirror on the IL surface during the deposition of Au, Pd and Ru. The deposition of Au and Pd NPs onto ILs containing NTf2- as counteranion was achieved by increasing the temperature, but only Pd led to the formation of small and well dispersed NPs (Figure 5). Interestingly, the deposition of small clusters was observed. We are currently investigating the mechanism of this process, since it can open up a new and promising field for the generation of extremely active catalytic systems. Once finished, this study will be submitted to a very high impact journal.
Work Package 3 (WP3) regarded the catalytic applications of the new systems MNPs-IL. Only the system consisting of PdNPs deposited onto IL 1 (Scheme 1) provided some enantioselectivity in the alcohol products obtained from hydrogenation of prochiral ketones. The best result was obtained in the hydrogenation of acetophenone, for which 20% of enantiomeric excess (ee) was observed. These results will be submitted to Chemical Communication as soon as an improvement in the %ee will be achieved.
Finally, Work package 4 and Work Package 5 are related to management, dissemination and communication (WP4), and training (WP5), respectively. I regularly promoted SDchirnanocat at group meetings, meetings at Departmental and Research Center level, and collaboration meetings. Finally, I delivered several oral presentations to communicate my research projects at different international conferences: (1) 43rd International Conference on Coordination Chemistry (Sendai, Japan, 2018); (2) 255th ACS National Meeting & Exposition. (New Orleans, U.S.A. 2018); (3) III International Symposium on Nanoparticles/Nanomaterials and Applications (Caparica, Portugal, 2018).
On the other hand, I have written as corresponding author all the articles associated to the research work performed during the development of SDchirnanocat: (1) Cat. Sci. Tech. 2018, 8, 221 (green open access); (2) Phys. Chem. Chem. Phys. 2018, 20, 20821 (gold open access under process); (3) Applied Catalysis: B Environmental (submitted, manuscript number APCATB-D-18-03867). I have supervised 3 Master and 3 PhD students, I have established different collaborations, and I have developed several proposals in order to apply for independent research positions. Finally, I attended to five short-courses offered by the University of Nottingham research training programme.
The outcomes achieved through the development of SDchirnanocat will contribute to broaden the knowledge of scientific community in the research fields of ILs, MNPs and catalysis, and can have an indubitable socioeconomic impact:
- The synthesis of new chiral ILs can promote the industrial innovation, since these compounds exhibit multiple applications, like ligand exchange chromatography, stereoselective polymerization, liquid and gas chromatography and capillary electrophoresis.
- The SD of MNPs onto ILs is a very new research area and the factors which control the formation mechanism of MNPs are not yet completely understood. Therefore, the study of such a mechanism will contribute to the advancement of an innovative research line with high potential, which will enhance the scientific output and competitiveness of European Union.
- The use of a physical technique such as SD methodology for the fast generation of catalytic systems MNPs-ILs with control of size and shape in an environmental friendly way (avoiding the use of organic solvents and reducing agents) can open a new venue for innovation and research in the field of sustainable catalysis and offer new solutions for one major issue of the current society, such as the generation of residues.
- To the best of our knowledge, this is the first example in which chiral MNPs-IL systems is generated via SD and applied in enantioselective catalysis. Thus, the research carried out in this project will expand the research fields of MNPs and catalysis.
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