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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 2 - NoNaCat (Development of Molecular-defined Non-noble Metal Complexes and Nano-structured Materials for Sustainable Redox ReactionsDevelopment of Molecular-defined Non-noble Metal Complexes and Nano-structured)

Teaser

The general goal of this project is to develop novel innovative base metal catalysts for green and sustainable transformations. Catalysis is a key technology for the European chemical industry as well as life science industries.

Summary

Work performed

Due to the inherent advantages of earth abundant metals there is an increasing interest in doing catalysis in the presence of such bio-relevant systems. In this respect, catalysis with non-noble metal complexes offers a highly attractive replacement. Hence, this area is increasingly attractive for homogeneous and heterogeneous catalysis. Within the ERC project NoNaCat novel molecularly-defined catalysts and nano-structured materials are prepared and explored for sustainable redox reactions. In the first year several interesting results have been achieved:
1. In our initial work, we demonstrated the first example of homogeneous non-noble metal-catalyzed transfer hydrogenations of N-heteroarenes. More specifically, we showed that the combination of simple cobalt salts with tris-2-(diphenylphosphino)-phenyl)phosphine L1 is able to selectively reduce quinolines in the presence of other sensitive functional groups, under mild conditions (Scheme1). Advantageously, these reductions can be performed without any external pressure simply using formic acid as a hydrogen source.

To be provided on demand = Scheme 1. Yield of product 2a in the transfer hydrogenation of quinoline (1a) using different reducing agents.

2. Most recently, we described the first heterogeneous single atom catalysts (SACs), which are conveniently prepared by decorating alumina nanorods with platinum atoms. The resulting stable material efficiently catalyzes hydrosilylation of industrially relevant olefins with high TON (â‰ˆ105) (Scheme 2). In general, such catalytic hydrosilylations represents a straightforward and atom-efficient methodology for the creation of Câˆ’Si bonds. While the application of homogeneous platinum complexes prevails in industry and academia, the new heterogeneous catalysts constitute state-of-the-art systems. A variety of substrates was selectively hydrosilylated including compounds with sensitive reducible and other functional groups (N, B, F, Cl). Notably, the single atom based catalyst shows significantly higher activity compared to related Pt nanoparticles.

To be provided on demand = Scheme 2. Pt-SAC show similar performance to best homogeneous Pt catalysts.

3. The first general and efficient non-noble metal-catalyzed reductive C2-alkoxylation of cyclic imides (phthalimides and succinimides) was achieved (Scheme 3). Crucial for the success was the use of a [Co(BF4)2Â·6H2O/Triphos] system. Using this catalyst, the hydrogenation of the aromatic ring of the parent phthalimide is avoided and only one of the carbonyl groups was selectively functionalized. The resulting products, N- and aryl-ring substituted 3-alkoxy-2,3-dihydro-1H-isoindolin-1-one and N-substituted 3-alkoxy-pyrrolidin-2-one derivatives were prepared under mild conditions in good to excellent isolated yields. Intramolecular reductive couplings can also be performed affording tricyclic compounds in one-step process. The new protocol opens the way to the development of different base-metal processes for the straightforward synthesis of functionalized N-heterocyclic compounds with pharmaceutical and biological interest.

To be provided on demand = Scheme 3. Selective Co-catalyzed reduction of phthalimides and succinimides.

4. In a microreview, we highlighted the importance of base-metal catalysis, especially with non-noble-metal pincer-type catalysts, which is increasingly used in organic synthesis and thus becoming more and more important for organometallic chemistry.

5. Hydrodehalogenation is a straightforward approach for detoxifications of harmful anthropogenic organohalide-based pollutants, as well as removal of halide protecting groups used in multistep syntheses. A novel sustainable catalytic material was prepared from biowaste (chitosan) in combination with an earth-abundant cobalt salt. This heterogeneous catalyst was fully characterized by transmission electron microscope, X-ray diffraction, and X-ray photoelectron spectroscopy measurements, and successfull

Final results

Within the first year new nano-structured materials as well as molecularly-defined complexes have been synthesized and characterized.
Several of these materials and complexes showed improved performance for catalytic reductions of nitriles and carboxylic acid derivatives compared to previously known materials. In addition, state-of-the-art catalysts for reductive aminations have been developed, which show unprecedented substrate scope.