Abstract
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 H2 metathesis as the rate-determining step.
Highlights
Catalytic reductive aminations and hydrogenations constitute essential processes widely applied in research laboratories and industries for the synthesis of ne and bulk chemicals as well as molecules used in life sciences
The Ni-triphos system was well tolerated with ammonia and due to strong coordination, and this PPP-ligand was found to be appropriate to avoid the formation of a Wernertype ammonia complex
In other tested solvents, we did not observe the formation of the desired product, primary amine 2
Summary
Catalytic reductive aminations and hydrogenations constitute essential processes widely applied in research laboratories and industries for the synthesis of ne and bulk chemicals as well as molecules used in life sciences. In particular, the selective and efficient synthesis of amines by applying these processes starting from inexpensive and available starting materials, and green and abundant reagents using non-noble metal-based catalysts continues to be an important goal of chemical research. In addition to synthetic applications, it is important to know the mode of action of Ni-complexes, formation of catalytically active species, and reactivity and selectivity towards reductive amination as well as their compatibility with ammonia. In this respect, here we report a Ni-linear triphos (bis(diphenylphosphinoethyl) phenylphosphine) complex as the rst homogeneous Ni-based catalyst for both reductive amination and hydrogenation of nitroarenes. In order to know the reactivity of other tridentate ligands, we tested
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