Homogeneous cobalt-catalyzed reductive amination for synthesis of functionalized primary amines

The development of earth abundant 3d metal-based catalysts continues to be an important goal of chemical research. In particular, the design of base metal complexes for reductive amination to produce primary amines remains as challenging. Here, we report the combination of cobalt and linear-triphos (bis(2-diphenylphosphinoethyl)phenylphosphine) as the molecularly-defined non-noble metal catalyst for the synthesis of linear and branched benzylic, heterocyclic and aliphatic primary amines from carbonyl compounds, gaseous ammonia and hydrogen in good to excellent yields. Noteworthy, this cobalt catalyst exhibits high selectivity and as a result the -NH2 moiety is introduced in functionalized and structurally diverse molecules. An inner-sphere mechanism on the basis of the mono-cationic [triphos-CoH]+ complex as active catalyst is proposed and supported with density functional theory computation on the doublet state potential free energy surface and H2 metathesis is found as the rate-determining step

Silica-supported Fe/Fe–O nanoparticles for the catalytic hydrogenation of nitriles to amines in the presence of aluminium additives

The hydrogenation of nitriles to amines represents an important and frequently used industrial process due to the broad applicability of the resulting products in chemistry and life sciences. Despite the existing portfolio of catalysts reported for the hydrogenation of nitriles, the development of iron-based heterogeneous catalysts for this process is still a challenge. Here, we show that the impregnation and pyrolysis of iron(II) acetate on commercial silica produces a reusable Fe/Fe-O@SiO2 catalyst with a well-defined structure comprising the fayalite phase at the Si-Fe interface and alpha-Fe nanoparticles, covered by an ultrathin amorphous iron(III) oxide layer, growing from the silica matrix. These Fe/Fe-O core-shell nanoparticles, in the presence of catalytic amounts of aluminium additives, promote the hydrogenation of all kinds of nitriles, including structurally challenging and functionally diverse aromatic, heterocyclic, aliphatic and fatty nitriles, to produce primary amines under scalable and industrially viable conditions.Web of Science51292

Synergy between homogeneous and heterogeneous catalysis

Catalysis plays a decisive role in the advancement of sustainable processes in chemical, pharmaceutical, and agrochemical industries as well as petrochemical, material, and energy technologies. Notably, more than 80% of all chemical products involve catalysis processes in at least one stage in their manufacture. Thus, for the modernization of chemical synthesis, the applicability of catalysts is crucial. Since the beginning of catalysis, a large number of both homogeneous and heterogeneous catalysts have been developed and applied for all kinds of synthetic reactions. Among these, homogeneous complexes are active and selective but not stable and they are difficult to recycle or reuse. On the other hand, heterogeneous materials are quite stable and conveniently recyclable, but they exhibit lower activity and selectivity. In catalysis, the development of ‘ideal’ catalysts, which should be more active and selective as well as stable and easily recyclable, is of prime importance to produce all kinds of chemicals including life science molecules. In order to develop such catalyst systems, combining both homogeneous and heterogeneous catalysis concepts is considered to be a promising strategy. Applying this approach, special kinds of catalysts such as nanoparticles and single atoms as well as supported homogeneous complexes can be designed. These types of catalysts can overcome the limitations of both molecularly defined complexes and traditional heterogeneous materials. In this respect, in recent years more focus has been paid to the design of these classes of catalysts for organic synthesis. Consequently, in this review, we discuss the application of synergies between homogeneous and heterogeneous catalysis concepts in developing suitable catalysts that exhibit both activity and selectivity as well as stability and reusability. More specifically, selected examples and key achievements made on the preparation and applications of nanoparticles, single atoms, and supported homogeneous complexes for organic transformations are summarized and discussed. © 2022 The Royal Society of Chemistry

A General Catalyst Based on Cobalt Core–Shell Nanoparticles for the Hydrogenation of N-Heteroarenes Including Pyridines

Herein, we report the synthesis of specific silica-supported Co/Co3O4 core–shell based nanoparticles prepared by template synthesis of cobalt-pyromellitic acid on silica and subsequent pyrolysis. The optimal catalyst material allows for general and selective hydrogenation of pyridines, quinolines, and other heteroarenes including acridine, phenanthroline, naphthyridine, quinoxaline, imidazo[1,2-a]pyridine, and indole under comparably mild reaction conditions. In addition, recycling of these Co nanoparticles and their ability for dehydrogenation catalysis are showcased. © 2020 The Authors. Published by Wiley-VCH Gmb

General and selective synthesis of primary amines using Ni-based homogeneous catalysts

The development of base metal catalysts for industrially relevant amination and hydrogenation reactions by applying abundant and atom economical reagents continues to be important for the cost-effective and sustainable synthesis of amines which represent highly essential chemicals. In particular, the synthesis of primary amines is of central importance because these compounds serve as key precursors and central intermediates to produce value-added fine and bulk chemicals as well as pharmaceuticals, agrochemicals and materials. Here we report a Ni-triphos complex as the first Ni-based homogeneous catalyst for both reductive amination of carbonyl compounds with ammonia and hydrogenation of nitroarenes to prepare all kinds of primary amines. Remarkably, this Ni-complex enabled the synthesis of functionalized and structurally diverse benzylic, heterocyclic and aliphatic linear and branched primary amines as well as aromatic primary amines starting from inexpensive and easily accessible carbonyl compounds (aldehydes and ketones) and nitroarenes using ammonia and molecular hydrogen. This Ni-catalyzed reductive amination methodology has been applied for the amination of more complex pharmaceuticals and steroid derivatives. Detailed DFT computations have been performed for the Ni-triphos based reductive amination reaction, and they revealed that the overall reaction has an inner-sphere mechanism with H2metathesis as the rate-determining step. © The Royal Society of Chemistry 2020

A General Catalyst Based on Cobalt Core–Shell Nanoparticles for the Hydrogenation of N‐Heteroarenes Including Pyridines

Herein, we report the synthesis of specific silica-supported Co/Co3O4 core–shell based nanoparticles prepared by template synthesis of cobalt-pyromellitic acid on silica and subsequent pyrolysis. The optimal catalyst material allows for general and selective hydrogenation of pyridines, quinolines, and other heteroarenes including acridine, phenanthroline, naphthyridine, quinoxaline, imidazo[1,2-a]pyridine, and indole under comparably mild reaction conditions. In addition, recycling of these Co nanoparticles and their ability for dehydrogenation catalysis are showcased. © 2020 The Authors. Published by Wiley-VCH Gmb

Ultra-small cobalt nanoparticles from molecularly-defined Co-salen complexes for catalytic synthesis of amines

We report the synthesis of in situ generated cobalt nanoparticles from molecularly defined complexes as efficient and selective catalysts for reductive amination reactions. In the presence of ammonia and hydrogen, cobalt-salen complexes such as cobalt(ii)-N,N′-bis(salicylidene)-1,2-phenylenediamine produce ultra-small (2-4 nm) cobalt-nanoparticles embedded in a carbon-nitrogen framework. The resulting materials constitute stable, reusable and magnetically separable catalysts, which enable the synthesis of linear and branched benzylic, heterocyclic and aliphatic primary amines from carbonyl compounds and ammonia. The isolated nanoparticles also represent excellent catalysts for the synthesis of primary, secondary as well as tertiary amines including biologically relevant N-methyl amines. This journal is © The Royal Society of Chemistry