Recent Advances in Transition Metal-Catalyzed Hydrogenation of Nitriles

Turning the product selectivity of nitrile hydrogenation from primary to secondary amines by precise modification of Pd/SiC catalysts using NiO nanodots

The selectivity of nitrile hydrogenation was turned by the concentration of hydrogen radicals on Pd surface.

Cobalt pincer complexes for catalytic reduction of nitriles to primary amines

An efficient cobalt pincer type complex catalyzes the hydrogenation of nitriles to amines under mild conditions with high yields.

Rhodium-catalyzed biheteroaryl-2-carbonitrile synthesis via double C–H activation

Rhodium(iii)-catalyzed double C–H activation and in situ dealcoholization to generate biheteroaryl-2-carbonitriles have been developed via a CDC mechanism, in which benzimidates act as both directing groups and the precursors of nitrile groups.

Thiocyanate radical mediated dehydration of aldoximes with visible light and air

This work describes the first example of dehydration of aldoximes by an in situ generated radical-based hydrogen abstraction reaction.

Interplay of nucleophilic catalysis with proton transfer in the nitrile reductase QueF from Escherichia coli

Proton relay through an active-site network of hydrogen bonds promotes enzymatic nitrile reduction to amine via a covalent thioimidate enzyme intermediate.

Mining of aminotransferase gene ota3 from Bacillus pumilus W3 via genome analysis, gene cloning and expressing for compound bioamination

Aminotransferases are widely employed as biocatalysts to produce chiral amines and biologically active pharmaceuticals via asymmetric synthesis. In this study, transaminase genes in the Bacillus pumilus W3 genome were analysed, and gene ota3 encoding a putative (R)-selective transaminase was identified. The sequence of ota3 shares highest sequence identity (24.7%) with the first (R)-selective aminotransferase from Arthrobacter sp. KNK 168. Amino acid sequence and conserved domains analyses indicated that ω-BPAT encoded by ota3 belonged to the pyridoxal 5'-phosphate-dependent class IV (PLPDE_IV) superfamily. Both native and codon-optimised ω-BPAT genes were recombinantly expressed, and the purified proteins had a molecular mass of ~33.4 kDa. Furthermore, enantioselectivity tests with (S)- and (R)-α-phenethylamine revealed its (R)-selectivity. The optimal conditions for catalytic reaction were 45 °C and pH 7.0, and ω-BPAT retained stability at 20 °C and pH 7.0. Thus, ω-BPAT is a novel (R)-selective aminotransferase with great potential as a universal biocatalyst.

Transition metal-catalyzed dehydrogenation of amines

This review focuses on the use of homogeneous transition metal complexes for the catalytic dehydrogenation of amines for synthetic purposes, and for hydrogen storage applications. The catalytic dehydrogenation of primary, secondary and cyclic amines is reviewed looking at reaction conditions, different catalysts and common side reactions. Recent developments in this active field of research showcase how cooperative ligands and photocatalysts can overcome the need for noble metals or harsh reaction conditions.

Cobalt-based nanoparticles prepared from MOF-carbon templates as efficient hydrogenation catalysts

Pyrolysis of cobalt-terephthalic acid MOF template on carbon produces highly active and selective cobalt nanoparticles-based hydrogenation catalysts.

The development of efficient and selective nanostructured catalysts for industrially relevant hydrogenation reactions continues to be an actual goal of chemical research. In particular, the hydrogenation of nitriles and nitroarenes is of importance for the production of primary amines, which constitute essential feedstocks and key intermediates for advanced chemicals, life science molecules and materials. Herein, we report the preparation of graphene shell encapsulated Co₃O₄- and Co-nanoparticles supported on carbon by the template synthesis of cobalt-terephthalic acid MOF on carbon and subsequent pyrolysis. The resulting nanoparticles create stable and reusable catalysts for selective hydrogenation of functionalized and structurally diverse aromatic, heterocyclic and aliphatic nitriles, and as well as nitro compounds to primary amines (>65 examples). The synthetic and practical utility of this novel non-noble metal-based hydrogenation protocol is demonstrated by upscaling several reactions to multigram-scale and recycling of the catalyst.

Pd-CuFe Catalyst for Transfer Hydrogenation of Nitriles: Controllable Selectivity to Primary Amines and Secondary Amines

A multicomponent nanocatalyst system was fabricated for the transfer hydrogenation of nitrile compounds. This catalyst system contains palladium, copper, and iron, which are supported on the magnetite nanospheres, and the loading of palladium could be at the parts per million level. Palladium and copper contribute to the transformation of nitrile, and the product distribution highly depends on the alloying of Fe to Cu. The nitriles could be converted to primary amine by the Pd-Cu catalyst in the absence of Fe, whereas in the presence of Fe the products are secondary amines with high selectivity. This could be attributed to the electronic modulation of iron to copper. A variety of nitriles have been transformed to the corresponding primary or secondary amines with high selectivity, and the TOF reaches 2,929 hr⁻¹ for Pd. Furthermore, the catalyst could be recycled by an external magnetic field and reused five times without severe activity loss.

•

The novel transfer hydrogenation of nitriles to primary or secondary amine

•

The dosage of Pd can be reduced to 139 ppm with a TOF of 3,597 hr⁻¹

•

The selectivity of products can be easily adjusted by electronic modulation

Reductive Deuteration of Nitriles: The Synthesis of α,α-Dideuterio Amines by Sodium-Mediated Electron Transfer Reactions

The first general reductive deuteration of nitriles under single-electron transfer conditions has been developed for the synthesis of α,α-dideuterio amines. This practical and cost-efficient protocol requires only bench stable and commercially available sodium dispersions and EtOD- d₁ and allows for the reductive deuteration of a variety of nitriles in excellent yields and deuterium incorporations.

Oxa-Michael Addition to α,β-Unsaturated Nitriles: An Expedient Route to γ-Amino Alcohols and Derivatives

Water addition to α,β-unsaturated nitriles would give facile access to the β-hydroxy-nitriles, which in turn can be hydrogenated to the γ-amino alcohols. We have previously shown that alcohols readily add in 1,4-fashion to these substrates using Milstein's Ru(PNN) pincer complex as catalyst. However, attempted water addition to α,β-unsaturated nitriles gave the 3-hydroxynitriles in mediocre yields. On the other hand, addition of benzyl alcohol proceeded in excellent yields for a variety of β-substituted unsaturated nitriles. Subsequent treatment of the benzyl alcohol addition products with TMSCl/FeCl3 resulted in the formation of 3-hydroxy-alkylnitriles. The 3-benzyloxy-alkylnitriles obtained from oxa-Michael addition also could be hydrogenated directly in the presence of acid to give the amino alcohols as their HCl salts in excellent yields. Hydrogenation under neutral conditions gave a mixture of the secondary and tertiary amines. Hydrogenation in the presence of base and Boc-anhydride gave the orthogonally bis-protected amino alcohols, in which the benzyl ether can subsequently be cleaved to yield Boc-protected amino alcohols. Thus, a variety of molecular scaffolds with a 1,3-relationship between O- and N-functional group is accessible starting from oxa-Michael addition of benzyl alcohol to α,β-unsaturated nitriles.

Selective Hydrogenation of Cyclic Imides to Diols and Amines and Its Application in the Development of a Liquid Organic Hydrogen Carrier

Direct hydrogenation of a broad variety of cyclic imides to diols and amines using a ruthenium catalyst is reported here. We have applied this strategy toward the development of a new liquid organic hydrogen carrier system based on the hydrogenation of bis-cyclic imide that is formed by the dehydrogenative coupling of 1,4-butanediol and ethylenediamine using a new ruthenium catalyst. The rechargeable system has a maximum gravimetric hydrogen storage capacity of 6.66 wt%.

Synthesis of cobalt nanoparticles by pyrolysis of vitamin B12: a non-noble-metal catalyst for efficient hydrogenation of nitriles

A facile preparation of vitamin B₁₂-derived carbonaceous cobalt particles supported on ceria is reported.

Cobalt-Catalyzed and Lewis Acid-Assisted Nitrile Hydrogenation to Primary Amines: A Combined Effort

The selective hydrogenation of nitriles to primary amines using a bench-stable cobalt precatalyst under 4 atm of H₂ is reported herein. The catalyst precursor was reduced in situ using NaHBEt₃, and the resulting Lewis acid formed, BEt₃, was found to be integral to the observed catalysis. Mechanistic insights gleaned from para-hydrogen induced polarization (PHIP) transfer NMR studies revealed that the pairwise hydrogenation of nitriles proceeded through a Co(I/III) redox process.

Designing metal-contained enzyme mimics for prodrug activation

Enzyme-activated prodrug therapy (EAPT) is a widely-used and effective treatment method for cancer by converting prodrugs into drugs at the demanded time and space, whose key step is prodrug activation. Traditional prodrug activations are mostly dependent on natural enzymes, which are unstable, expensive and hard to be functionalized. The emerging enzyme mimics, especially the metal-contained enzyme mimics (MEMs), provide a potential chance for improving the traditional EAPT because of their high stability, low cost and easiness of preparation and functionalization. The existing MEMs can be classified into three categories: catalytic core-scaffold MEM (csMEM), nanoparticle MEM (npMEMs) and metal-organic framework (MOF) MEM (mofMEM). These MEMs can mimic diverse functions corresponding to natural enzymes, and some of which are potentially used in prodrug activation, such as DNase, RNase, carbonate esterase, etc. In this review, we briefly summarize the MEMs according to their structure and composition, and highlight the successful and potential applications for prodrug activation mediated by hydrolase-like and oxidoreductase-like MEMs.

Nickel-Catalyzed Transfer Hydrogenation of Benzonitriles with 2-Propanol and 1,4-Butanediol as the Hydrogen Source

The homogeneous transfer hydrogenation of benzonitrile with 2-propanol or 1,4-butanediol produced N-benzylidene benzylamine (BBA, 85% yield) using 5 mol % [Ni(COD)2] as a catalytic precursor and a mixture of Cy2P(CH2)2PCy2 and Cy2P(CH2)2P(O)Cy2 as ancillary ligands, under mild reaction conditions (120 °C, 96 h, tetrahydrofuran). 1,4-Butanediol performed better than 2-propanol as a hydrogen donor and yielded γ-butyrolactone as the product of transfer dehydrogenation. Selectivity toward dibenzylamine (DBA, 62% yield) was achieved by varying the amount of 1,4-butanediol in the catalytic system. A reaction mechanism was proposed, involving a ligand-assisted O-H bond activation, end-on substrate coordination, and a key dihydrido-Ni(II) intermediate, leading to the in situ formation of primary imines and amines to ultimately yield the secondary imines observed.

Selective Hydrogenation of Nitriles to Primary Amines by using a Cobalt Phosphine Catalyst

A general procedure for the catalytic hydrogenation of nitriles to primary amines by using a non-noble metal-based system is presented. Co(acac)₃ in combination with tris[2-(dicyclohexylphosphino)ethyl]phosphine efficiently catalyzes the selective hydrogenation of a wide range of (hetero)aromatic and aliphatic nitriles to give the corresponding amines.

Selective Hydrogenation of Nitriles to Primary Amines Catalyzed by a Polysilane/SiO2-Supported Palladium Catalyst under Continuous-Flow Conditions

Hydrogenation of nitriles to primary amines with heterogeneous catalysts under liquid‐phase continuous‐flow conditions is described. Newly developed polysilane/SiO₂‐supported Pd was found to be an effective catalyst and various nitriles were converted into primary amine salts in almost quantitative yields under mild reaction conditions. Interestingly, a complex mixture was obtained under batch conditions. Lifetime experiments showed that this catalyst remained active for more than 300 h (TON≥10 000) without loss of selectivity and no metal leaching from the catalyst occurred. By using this continuous‐flow hydrogenation, synthesis of venlafaxine, an antidepressant drug, has been accomplished.

Efficient and selective hydrogenation of benzonitrile to benzylamine: improvement on catalytic performance and stability in a trickle-bed reactor

The hydrogenation of benzonitrile with a high benzylamine yield of 86% is accomplished over a Pd/γ-Al₂O₃ catalyst in a trickle-bed reactor.

An expedient and novel strategy for reductive amination by employing H2O as both a hydrogen source and solventviaB2(OH)4/H2O systems

An efficient, convenient and mild Ru-catalyzed reductive amination reaction was developed by employing H₂O as both hydrogen source and solventviaB₂(OH)₄/H₂O systems. α-Deuterated amines were also obtained expediently by employing D₂O in our catalytic systems.