Ruthenium/Imidazolylphosphine Catalysis: Hydrogenation of Aliphatic and Aromatic Nitriles to Form Amines

Efficient Hydrogenation of N-Heterocycles Catalyzed by NNP-Manganese(I) Pincer Complexes at Ambient Temperature

Manganese-catalyzed hydrogenation reactions have aroused widespread interest in recent years. Among the catalytic systems described, especially PNP- and NNP-Mn pincer catalysts have been reported for the hydrogenation of aldehydes, ketones, nitriles, aldimines and esters. Furthermore, NNP-Mn pincer compounds are efficient catalysts for the hydrogenolysis of less reactive amides, ureas, carbonates, and carbamates. Herein, the synthesis and application of specific imidazolylaminophosphine ligands and the corresponding Mn pincer complexes are described. These new catalysts have been characterized and studied by a combination of experimental and theoretical investigations, and their catalytic activities have been tested in several hydrogenation reactions with good to excellent performance. Especially, the reduction of N-heterocycles can be performed under very mild conditions.

Metal/Non-Metal Catalyzed Activation of Organic Nitriles

Nitrile activation is a prominent topic in recent developments in chemistry, especially in organic, inorganic, biological chemistry, as well as in the natural synthesis of products and in the pharmaceutical industry. The activation of nitriles using both metal and non-metal precursors has attracted several researchers, who are exploring newer ways to synthesize novel compounds. Nitrile activation can be achieved by combining various catalytic double hydroelementation reactions, such as hydrosilylation, hydroboration, and hydrogenation of organonitriles using silanes, pinacolborane, and other sources of hydrogen. These methodologies have garnered considerable attention since they are effective in the reduction of organonitriles, whose end products are extensively applied in synthetic organic chemistry. In this review, we summarize the development of selective hydroborylation, hydrosilylation, dihydroborysilylation, and hydrogenation of organonitriles, as well as their reaction mechanisms and the role of metal complexes in the catalytic cycles. This review article explains various synthetic methodologies applied toward the reduction of organonitriles into corresponding amines.

Heterogeneous Catalytic Hydrogenation of 3-Phenylpropionitrile over Palladium on Carbon

A previously developed and industrially feasible process for selective, Pd-mediated, liquid-phase heterogeneous catalytic hydrogenation of nitriles to primary amines was extended to the reduction of 3-phenylpropionitrile (PPN) to 3-phenylpropylamine (PPA). PPN, which belongs to the homologous series of benzonitrile (BN) and benzyl cyanide (BC), was hydrogenated under mild reaction conditions (30-80 °C, 6 bar), over Pd/C, in two immiscible solvents (dichloromethane/water) and using acidic additives (NaH₂PO₄ and H₂SO₄). Although relatively high conversion (76%) was achieved, the selectivity to PPA (26%) and its isolated yield (20%) were lesser than those in the case of the hydrogenation of BN or BC reported earlier. However, the purity of PPA was >99% without using any purification method. Quantum chemical calculations using a density functional theory (DFT) method were performed to compare the adsorption interactions of the different imine intermediates on palladium, as well as to clarify the differences observed in the primary amine selectivity. PPA is a valuable intermediate for the synthesis of carboxypeptidase B enzyme inhibitors, antimuscarinic drugs, or potential anticancer agents in the pharmaceutical industry.

Highly selective hydrogenation of aldehydes promoted by a palladium-based catalyst and its application in equilibrium displacement in a one-enzyme procedure using ω-transaminase

A palladium-based catalyst-promoted highly selective hydrogenation of aldehydes and its application in efficient equilibrium displacement in a one-enzyme procedure using ω-transaminase.

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.

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.

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.

Nitrile hydroboration reactions catalysed by simple nickel salts, bis(acetylacetonato)nickel(ii) and its derivatives

Simple nickel salts, bis(acetylacetonato)nickel(ii) and its derivatives, catalyzed the hydroboration reactions of aryl and alkyl nitriles with catechol borane.

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.

Stable and Inert Cobalt Catalysts for Highly Selective and Practical Hydrogenation of C≡N and C═O Bonds

Novel heterogeneous cobalt-based catalysts have been prepared by pyrolysis of cobalt complexes with nitrogen ligands on different inorganic supports. The activity and selectivity of the resulting materials in the hydrogenation of nitriles and carbonyl compounds is strongly influenced by the modification of the support and the nitrogen-containing ligand. The optimal catalyst system ([Co(OAc)2/Phen@α-Al2O3]-800 = Cat. E) allows for efficient reduction of both aromatic and aliphatic nitriles including industrially relevant dinitriles to primary amines under mild conditions. The generality and practicability of this system is further demonstrated in the hydrogenation of diverse aliphatic, aromatic, and heterocyclic ketones as well as aldehydes, which are readily reduced to the corresponding alcohols.

Selective hydrogenation of nitriles to primary amines catalyzed by a novel iron complex

Hydrogenation of nitriles to primary amines constitutes an atom-efficient and environmentally benign synthetic reaction. Herein we present a novel complex based on earth-abundant iron, and its application in the catalytic homogeneous hydrogenation of (hetero)aromatic, benzylic, and aliphatic nitriles to selectively form primary amines.

Copper-catalyzed decarboxylative cross-coupling of cinnamic acids and ACCN via single electron transfer

A novel and convenient method for the synthesis of β,γ-unsaturated nitriles using ACCN (1,1′-azobis(cyclohexane-1-carbonitrile)) as a cyano source was described.

Selective catalytic hydrogenation of nitriles to primary amines using iron pincer complexes

The selective catalytic hydrogenation of nitriles to primary amines with the well-defined Fe(PNP^Cy) pincer complex 2 is reported.

Magnesium-catalysed nitrile hydroboration

A β-diketiminato n-butylmagnesium complex is presented as a selective precatalyst for the reductive hydroboration of organic nitriles with pinacolborane (HBpin).

A β-diketiminato n-butylmagnesium complex is presented as a selective precatalyst for the reductive hydroboration of organic nitriles with pinacolborane (HBpin). Stoichiometric reactivity studies indicate that catalytic turnover ensues through the generation of magnesium aldimido, aldimidoborate and borylamido intermediates, which are formed in a sequence of intramolecular nitrile insertion and inter- and intramolecular B–H metathesis events. Kinetic studies highlight variations in mechanism for the catalytic dihydroboration of alkyl nitriles, aryl nitriles bearing electron withdrawing (Ar(EWG)CN) and aryl nitriles bearing electron donating (Ar(EDG)CN) substitution patterns. Kinetic isotope effects (KIEs) for catalysis performed with DBpin indicate that B–H bond breaking and C–H bond forming reactions are involved in the rate determining processes during the dihydroboration of alkyl nitriles and Ar(EDG)CN substrates, which display divergent first and second order rate dependences on [HBpin] respectively. In contrast, the hydroboration of Ar(EWG)CN substrates provides no KIE and HBpin is not implicated in the rate determining process during catalysis. Irrespective of these differences, a common mechanism is proposed in which the rate determining steps are deduced to vary through the establishment of several pre-equilibria, the relative positions of which are determined by the respective stabilities of the dimeric and monomeric magnesium aldimide and magnesium aldimidoborate intermediates as a result of adjustments to the basicity of the nitrile substrate. More generally, these observations indicate that homogeneous processes performed under heavier alkaline earth catalysis are likely to demonstrate previously unappreciated mechanistic diversity.

Formation and nitrile hydrogenation performance of Ru nanoparticles on a K-doped Al2O3 surface

Decarbonylation-promoted Ru nanoparticle formation from Ru₃(CO)₁₂ on a basic K-doped Al₂O₃ surface was investigated by in situ FT-IR and in situ XAFS. The prepared Ru nanoparticle acted as an efficient catalyst for nitrile hydrogenation to primary amine.

Mild and selective hydrogenation of aromatic and aliphatic (di)nitriles with a well-defined iron pincer complex

The catalytic hydrogenation of carboxylic acid derivatives represents an atom-efficient and clean reduction methodology in organic chemistry. More specifically, the selective hydrogenation of nitriles offers the possibility for a green synthesis of valuable primary amines. So far, this transformation lacks of useful, broadly applicable non-noble metal-based catalyst systems. In the present study, we describe a molecular-defined iron complex, which allows for the hydrogenation of aryl, alkyl, heterocyclic nitriles and dinitriles. By using an iron PNP pincer complex, we achieve very good functional group tolerance. Ester, ether, acetamido as well as amino substituents are not reduced in the presence of nitriles. Moreover, nitriles including an α,β-unsaturated double bond and halogenated derivatives are well tolerated in this reaction. Notably, our complex constitutes the first example of an homogeneous catalyst, which permits the selective hydrogenation of industrially important adipodinitrile to 1,6-hexamethylenediamine.