A General and Environmentally Benign Catalytic Reduction of Nitriles to Primary Amines

Abstract

Dedicated to Professor Günther Oehme on the occasion of his 70th birthdayA vast number of amines are produced by both the bulk and fine chemical industries, and a plethora of naturally occurring nitrogen compounds, such as alkaloids, amino acids, and nucleotides, play a pivotal role in biological processes. [1] During recent decades, several novel catalytic methods have been established for the synthesis of amines, such as palladium-catalyzed amination of aryl halides, [2] hydroaminations [3] and hydroaminomethylation of olefins or alkynes, [4] and homogeneous reductive aminations. [5] Nevertheless, the development of new and improved methods for the efficient and selective production of amines continues to be a challenging goal. Among the different known methods used, reductions are probably the most important due to the availability of starting materials (aldehydes, ketones, amides), price (hydrogen), and high atom efficiency. In this respect, the catalytic hydrogenation of nitriles also offers an interesting means of access to amines, which is used in industry for several products. In organic synthesis, nitriles are commonly reduced with stoichiometric amounts of metal hydrides, or in the presence of heterogeneous catalysts based on Pd, Ni, Co, etc. The former approach is expensive and not environmentally benign (over-stoichiometric amounts of waste), whereas the latter has limitations with respect to functional group tolerance and the excess of ammonia needed for high chemoselectivity. Surprisingly, the homoge-Herein, we describe for the first time the successful application of an easy-to-adopt catalytic system formed from commercially available [RuA C H T U N G T R E N N U N G (cod)methylallyl 2 ] (cod = 1,5-cyclooctadiene) and DPPF (1,1-bis(diphenylphosphino)ferrocene) for the homogeneous hydrogenation of a variety of aromatic and aliphatic nitriles, with excellent catalyst activity and high chemoselectivity. Scheme 1. Selectivity in the catalytic reduction of nitriles.

Tuning the selectivity of ruthenium nanoscale catalysts with functionalised ionic liquids: Hydrogenation of nitriles

“…Moreover, it is well known that the hydrogenation of PhCN to benzylamine is catalysed by molecular complexes [22][23][24]. In the case of metal surfaces [20,21,25] the activated amine -benzylamine -is rapidly transformed into the benzylidene benzylamine via aminolysis and coupling although we were unable to detect neither benzylamine nor benzylimine by ESI-MS and NMR experiments.…”

“…In the case of metal surfaces [20,21,25] the activated amine -benzylamine -is rapidly transformed into the benzylidene benzylamine via aminolysis and coupling although we were unable to detect neither benzylamine nor benzylimine by ESI-MS and NMR experiments. As already pointed out benzylamine undergoes exclusively aminolysis with solid catalysts, in contrast molecular catalysts give benzylamine as main product [22][23][24].…”

Selective Catalytic Reductions of Amides and Nitriles to Amines

“…Even better catalytic performance and functional group tolerance was obtained with an easily accessible in situ catalyst composed of [Ru(cod)methylallyl 2 ] and DPPF [53]. Here, under optimized conditions, a superior catalyst activity with a turnover frequency (TOF) of up to 5783 h -1 has been achieved in the hydrogenation of the benchmark substrate.…”

A Practical and Benign Synthesis of Primary Amines through Ruthenium‐Catalyzed Reduction of Nitriles

“…[15,17] Recently, we demonstrated that an in situ catalyst system composed of [RuA C H T U N G T R E N N U N G (cod)(methylallyl 2 )] (cod = 1,5-cyclooctadiene) and 1,1'-bis(diphenylphosphino)ferrocene (dppf) allows for excellent chemoselectivities (> 99 %) towards primary amines and high turnover frequencies up to 5783 h À1 . [18] Herein, we report our ongoing studies of the catalytic reduction of nitriles. For the first time, it is shown that straightforward ruthenium complexes modified by cheap and available triphenylphosphine allow for the efficient and general reduction of various kinds of aryl and alkyl nitriles.…”