Amine Catalyst Research Articles

Single-Crystal Cobalt Phosphide Nanorods as a High-Performance Catalyst for Reductive Amination of Carbonyl Compounds.

The development of metal phosphide catalysts for organic synthesis is still in its early stages. Herein, we report the successful synthesis of single-crystal cobalt phosphide nanorods (Co2P NRs) containing coordinatively unsaturated Co–Co active sites, which serve as a new class of air-stable, highly active, and reusable heterogeneous catalysts for the reductive amination of carbonyl compounds. The Co2P NR catalyst showed high activity for the transformation of a broad range of carbonyl compounds to their corresponding primary amines using an aqueous ammonia solution or ammonium acetate as a green amination reagent at 1 bar of H2 pressure; these conditions are far milder than previously reported. The air stability and high activity of the Co2P NRs is noteworthy, as conventional Co catalysts are air-sensitive (pyrophorous) and show no activity for this transformation under mild conditions. P-alloying is therefore of considerable importance for nanoengineering air-stable and highly active non-noble-metal catalysts for organic synthesis.

Phosphine ligands in the ruthenium-catalyzed reductive amination without an external hydrogen source

A systematic study of the phosphine additives influence on the activity of a ruthenium catalyst in reductive amination without an external hydrogen source was carried out. [CymeneRuCl2]2 was used as a reference catalyst, and a broad set of phosphines including Alk3P, Alk2ArP, Ar3P and X3P was screened. Three complexes of general formula (Cymene)RuCl2PR3 were isolated in a pure form, and their catalytic activity was compared with the in situ generated complexes. Nonhindered triarylphosphines with electron acceptor groups were found to be the most perspective activating agents, increasing the activity of the catalyst approx. six times, Alk2ArP ligands have less noticeable influence, while trialkylphosphines strongly deactivate the ruthenium catalyst.

Influence of Brønsted acid sites on chemoselective synthesis of pyrrolidones over H-ZSM-5 supported copper catalyst

Cu(0)/H-ZSM-5 was identified as a chemoselective catalyst in the reductive amination of levulinic acid for the synthesis of pyrrolidones at ambient pressure and in aqueous media. The chemoselective nature of Cu was explained by carbonyl interaction with surface Brønsted acid sites deduced by pyridine and acetone adsorbed in situ infrared (IR) spectroscopic studies in conjunction with N2O titration. A strong polarization of band at 1685 cm−1 and an increase in its intensity with a decrease in Si/Al ratio of the H-ZSM-5 was found to be a key factor in the reductive amination activity. Structure activity relationship was established using the physicochemical characteristics of the catalysts analyzed by XRD, BET-SA, H2-TPR, NH3-TPD and XPS analyses.

Cobalt encapsulated in N‑doped graphene sheet for one-pot reductive amination to synthesize secondary amines

To develop an efficient base-metal reductive amination catalyst for synthesis of secondary amines is still a major challenge. In this study, an efficient N-doped graphene sheet-coated cobalt catalyst ([email protected]) was developed through a simple pyrolysis process, which could gave 99.5 % yield of N-benzylaniline by one-pot reductive amination of nitrobenzene with benzaldehyde during at least 5 cycles. Catalyst characterization and control experiments confirmed that the robust catalytic performance of the catalyst is probably due to the synergy effect of in situ generated Co-Nx encapsulated in N‑doped graphene layer and appropriate meso-pore structure. Additionally, The substrate adaptability of the catalyst was proved since a variety of corresponding secondary amines were smoothly obtained under relatively mild conditions, which makes the secondary amine synthesis strategy based on [email protected] shows excellent application prospect.

Air Stable Iridium Catalysts for Direct Reductive Amination of Ketones.

Half-sandwich iridium complexes bearing bidentate urea-phosphorus ligands were found to catalyze the direct reductive amination of aromatic and aliphatic ketones under mild conditions at 0.5 mol % loading with high selectivity towards primary amines. One of the complexes was found to be active in both the Leuckart-Wallach (NH4 CO2 H) type reaction as well as in the hydrogenative (H2 /NH4 AcO) reductive amination. The protocol with ammonium formate does not require an inert atmosphere, dry solvents, as well as additives and in contrast to previous reports takes place in hexafluoroisopropanol (HFIP) instead of methanol. Applying NH4 CO2 D or D2 resulted in a high degree of deuterium incorporation into the primary amine α-position.

Organocatalyzed Cascade Aza-Michael/Aldol Reaction for Atroposelective Construction of 4-Naphthylquinoline-3-carbaldehydes.

An organocatalyzed cascade aza-Michael/Aldol reaction of alkynals with N-(2-(1-naphthoyl)phenyl)benzenesulfonamides has been disclosed. In the presence of a secondary amine catalyst, this method enables the construction of a series of axially chiral 4-naphthylquinoline-3-carbaldehydes in yields of up to 97% with enantioselectivities of up to 96%. Several further transformations of the synthesized products were investigated to demonstrate their synthetic applications.

Facile Synthesis of COF-Supported Reduced Pd-Based Catalyst for One-Pot Reductive Amination of Aldehydes

Dibenzylamine motifs are an important class of crucial organic compounds and are widely used in fine chemical and pharmaceutical industries. The development of the efficient, economical, and environmentally friendly synthesis of amines using transition metal-based heterogeneous catalysts remains both desirable and challenging. Herein, we prepared the covalent organic framework (COF)-supported heterogeneous reduced COF-supported Pd-based catalyst and used it for the one-pot reductive amination of aldehydes. There are both Pd metallic state and oxidated Pdσ+ in the catalysts. Furthermore, in the presence of the reduced COF-supported Pd-based catalyst, many aromatic, aliphatic, and heterocyclic aldehydes with various functional groups substituted were converted to their corresponding amines products in good to excellent selectivity (up to 91%) under mild reaction conditions (70 °C, 2 h, NH3, 20 bar H2). This work expands the covalent organic frameworks for the material family and its support catalyst, opening up new catalytic applications in the economical, practical, and effective synthesis of secondary amines.

Metal-based Heterogeneous Catalysts for One-Pot Synthesis of Secondary Anilines from Nitroarenes and Aldehydes.

Recently, N-substituted anilines have been the object of increasing research interest in the field of organic chemistry due to their role as key intermediates for the synthesis of important compounds such as polymers, dyes, drugs, agrochemicals and pharmaceutical products. Among the various methods reported in literature for the formation of C–N bonds to access secondary anilines, the one-pot reductive amination of aldehydes with nitroarenes is the most interesting procedure, because it allows to obtain diverse N-substituted aryl amines by simple reduction of nitro compounds followed by condensation with aldehydes and subsequent reduction of the imine intermediates. These kinds of tandem reactions are generally catalyzed by transition metal-based catalysts, mainly potentially reusable metal nanoparticles. The rapid growth in the last years in the field of metal-based heterogeneous catalysts for the one-pot reductive amination of aldehydes with nitroarenes demands for a review on the state of the art with a special emphasis on the different kinds of metals used as catalysts and their recyclability features.

Highly selective Ru/HBEA catalyst for the direct amination of fatty alcohols with ammonia

The present study describes the synthesis of primary amines from long-chain fatty alcohols and ammonia using supported ruthenium catalysts over different acid supports, including a variety of zeolites with different topologies and Si/Al ratios. The morphology, acidity and location of ruthenium in the catalysts was studied in detail by combining XRD, BET, HR-TEM, NH3-TPD, octylamine-TPD, H2-TPR, XPS, EXAFS / XANES, 27Al MAS NMR and TGA. In particular, Ru/HBEA (Si/Al = 25) with 5 wt% Ru afforded more than 90 % conversion and 90 % selectivity to 1-octylamine in the liquid-phase amination reaction of 1-octanol with ammonia at 180 °C in a batch reactor. The high selectivity of Ru/HBEA (Si/Al = 25) can be explained by the presence of Brønsted / Lewis acid centers with medium strength in the proximity of ruthenium nanoparticles. The catalyst was further tested in a pre-pilot continuous stirred-tank reactor (2 L) with flash separation of 1-octylamine. In this configuration, a steady 92 % selectivity of octylamine was obtained at 87 % 1-octanol conversion during 120 h on steam. The catalyst kept its integrity during the reaction.

A General Organocatalytic System for Enantioselective Radical Conjugate Additions to Enals

AbstractHerein, we report a general iminium ion‐based catalytic method for the enantioselective conjugate addition of carbon‐centered radicals to aliphatic and aromatic enals. The process uses an organic photoredox catalyst, which absorbs blue light to generate radicals from stable precursors, in combination with a chiral amine catalyst, which secures a consistently high level of stereoselectivity. The generality of this catalytic platform is demonstrated by the stereoselective interception of a wide variety of radicals, including non‐stabilized primary ones which are generally difficult to engage in asymmetric processes. The system also served to develop organocatalytic cascade reactions that combine an iminium‐ion‐based radical trap with an enamine‐mediated step, affording stereochemically dense chiral products in one‐step.

A General Organocatalytic System for Enantioselective Radical Conjugate Additions to Enals.

Herein, we report a general iminium ion‐based catalytic method for the enantioselective conjugate addition of carbon‐centered radicals to aliphatic and aromatic enals. The process uses an organic photoredox catalyst, which absorbs blue light to generate radicals from stable precursors, in combination with a chiral amine catalyst, which secures a consistently high level of stereoselectivity. The generality of this catalytic platform is demonstrated by the stereoselective interception of a wide variety of radicals, including non‐stabilized primary ones which are generally difficult to engage in asymmetric processes. The system also served to develop organocatalytic cascade reactions that combine an iminium‐ion‐based radical trap with an enamine‐mediated step, affording stereochemically dense chiral products in one‐step.

8+2] vs [4+2] Cycloadditions of Cyclohexadienamines to Tropone and Heptafulvenes—Mechanisms and Selectivities

The cinchona-alkaloid-catalyzed cycloaddition reactions of 2-cyclohexenone with tropone and various heptafulvenes give [8+2] or [4+2] cycloadducts, depending on the substituents present on the heptafulvene. We report the results of new experiments with heptafulvenes, containing diester and barbiturate substituents, which in combination with computational studies were performed to elucidate the factors controlling [8+2] vs [4+2] cycloaddition pathways, including chemo-, regio-, and stereoselectivities of these higher-order cycloadditions. The protonated cinchona alkaloid primary amine catalyst reacts with 2-cyclohexenone to form a linear dienamine intermediate that subsequently undergoes a stepwise [8+2] or [4+2] cycloaddition. Both tropone and the different heptafulvenes initially form [8+2] cycloadducts. The final product is ultimately decided by the reversibility of the [8+2] cycloaddition and the relative thermal stability of the [4+2] products. The stereoisomeric transition states are distinguished by the steric interactions between the protonated catalyst and tropone/heptafulvenes. The [8+2] cycloaddition of barbiturate-heptafulvene afforded products with an unprecedented trans-fusion of the five- and six-membered rings, while the [8+2] cycloadducts obtained from cyanoester-heptafulvene and diester-heptafulvene were formed with a cis-relationship. The mechanism, thermodynamics, and origins of stereoselectivity were explained through DFT calculations using the ωB97X-D density functional.

Synthesis of N-heterocyclic carbene-Pd(II)-5-phenyloxazole complexes and initial studies of their catalytic activity toward the Buchwald-Hartwig amination of aryl chlorides

Three new N-heterocyclic carbene (NHC)-Pd(II) complexes using 5-phenyloxazole as the ancillary ligand have been obtained in moderate to good yields by a one-pot reaction of the corresponding imidazolium salts, palladium chloride and 5-phenyloxazole under mild conditions. Initial studies showed that one of the complexes is an efficient catalyst for the Buchwald-Hartwig amination of aryl chlorides with various secondary and primary amines under the varied catalyst loading of 0.01-0.05 mol%, thus it will enrich the chemistry of NHCs and give an alternative catalyst for the coupling of challenging while cost-low aryl chlorides.

Organocatalytic Asymmetric Synthesis of Benzothiazolopyrimidines via [4 + 2] Cyclization of 2-Benzothiazolimines and Aldehydes.

We report the direct asymmetric synthesis of pyrimido[2,1-b]benzothiazoles using a commercially available chiral amine catalyst. A variety of 2-benzothiazolimines and aldehydes were well tolerated under the reaction conditions and generated the corresponding products in 81-99% yields with excellent diastereoselectivities and enantioselectivities (up to >20:1 dr, 99% ee). Furthermore, the products could be easily converted to other useful chiral building blocks.

Chiral Primary Amine/Ketone Cooperative Catalysis for Asymmetric α-Hydroxylation with Hydrogen Peroxide.

Carbonyls and amines are yin and yang in organocatalysis as they mutually activate and transform each other. These intrinsically reacting partners tend to condense with each other, thus depleting their individual activity when used together as cocatalysts. Though widely established in many prominent catalytic strategies, aminocatalysis and carbonyl catalysis do not coexist well, and, as such, a cooperative amine/carbonyl dual catalysis remains essentially unknown. Here we report a cooperative primary amine and ketone dual catalytic approach for the asymmetric α-hydroxylation of β-ketocarbonyls with H2O2. Besides participating in the typical enamine catalytic cycle, the chiral primary amine catalyst was found to work cooperatively with a ketone catalyst to activate H2O2 via an oxaziridine intermediate derived from an in-situ-generated ketimine. Ultimately, this enamine-oxaziridine coupling facilitated the highly controlled α-hydroxylation of several β-ketocarbonyls in excellent yield and enantioselectivity. Notably, late-stage hydroxylation for peptidyl amide or chiral esters can also be achieved with high stereoselectivity. In addition to its operational simplicity and mild conditions, this cooperative amine/ketone catalytic approach also provides a new strategy for the catalytic activation of H2O2 and expands the domain of typical amine and carbonyl catalysis to include this challenging transformation.

Regioselective benzoylation of unprotected β-glycopyranosides with benzoyl cyanide and an amine catalyst – application to saponin synthesis

Regioselective protection of trans-trans triol and tetrol moieties in carbohydrates was achieved with BzCN as the benzoylating agent and amine catalysts. The protocols are useful for the chemical synthesis of oligosaccharides and saponins.

RETRACTED ARTICLE: The amine-catalysed Suzuki–Miyaura-type coupling of aryl halides and arylboronic acids

Suzuki–Miyaura coupling is a practical and attractive carbon−carbon bond formation reaction due to its high efficiency and wide functional group compatibility, but its industrial applications are limited because it is typically catalysed by expensive palladium-containing transition-metal complexes. Here we show a robust and chemoselective organocatalytic Suzuki−Miyaura-type coupling of aryl halides with arylboronic acids catalysed by amines. The utility and scope of this reaction were demonstrated by the synthesis of several commercially relevant small molecules and a selection of derivatives of pharmaceutical drugs. The coupling of aryl halides and arylboronic acids is generally performed by metal-catalysed Suzuki–Miyaura reactions while metal-free approaches remain elusive. Here an organocatalytic approach based on amine catalysts is introduced for the preparation of commercially relevant asymmetric biaryls.

Exploring alkaline routes for production of TEOS-based consolidants for carbonate stones using amine catalysts

TEOS-based sols following basic catalysis routes were explored and showed high potential and important advantages for consolidation of soft limestone.

BF3·Et2O as a metal-free catalyst for direct reductive amination of aldehydes with amines using formic acid as a reductant

A versatile metal- and base-free direct reductive amination of aldehydes with primary and secondary amines catalyzed by inexpensive BF3·Et2O using formic acid as a reductant has been developed.

Oxovanadium(v)-catalyzed amination of carbon dioxide under ambient pressure for the synthesis of ureas.

Carbon dioxide is regarded as a reliable C1 building block in organic synthesis because of the nontoxic, abundant, and economical characteristics of carbon dioxide. In this manuscript, a commercially available oxovanadium(v) compound was demonstrated to serve as an efficient catalyst for the catalytic amination of carbon dioxide under ambient pressure in the synthesis of ureas. The catalytic transformation of chiral amines into the corresponding chiral ureas without loss of chirality was also performed. Furthermore, a gram-scale catalytic urea synthesis under ambient pressure was successfully achieved to validate the scalability of this catalytic activation of carbon dioxide.