N-Methylation of Amines with Methanol in Aqueous Solution Catalyzed by a Water-Soluble Metal–Ligand Bifunctional Dinuclear Iridium Catalyst

Selective Conversion of Glycerol to Lactic Acid in Water via Acceptorless Dehydrogenation Catalyzed by a Water-Soluble Metal-Ligand Bifunctional Iridium Catalyst

An efficient method for the selective conversion of glycerol, the major byproduct of the biodiesel manufacturing process, to lactic acid in water via acceptorless dehydrogenation has been developed. In the presence of a water-soluble [Cp*Ir(6,6'-(OH)2-2,2'-bpy)(H2O)][OTf]2 (0.1 mol %) and KOH (1.1 equiv), the reaction proceeded at 120 °C for 24 h to afford the desired product in >99% yield with >99% selectivity. It was confirmed that OH functional groups in the ligand were crucial for the activity of the iridium complex. Furthermore, density functional theory calculations and mechanistic experiments were also undertaken.

Ruthenium Complexes with NNN-Pincer Ligands for N-Methylation of Amines Using Methanol

A series of ruthenium complexes (Ru1-Ru4) bearing new NNN-pincer ligands were synthesized in 58-78% yields. All of the complexes are air and moisture stable and were characterized by IR, NMR, and high-resolution mass spectra (HRMS). In addition, the structures of Ru1-Ru3 were confirmed by X-ray crystallographic analysis. These Ru(II) complexes exhibited high catalytic efficiency and broad functional group tolerance in the N-methylation reaction of amines using CH3OH as both the C1 source and solvent. Experimental results indicated that the electronic effect of the substituents on the ligands considerably affects the catalytic reactivity of the complexes in which Ru3 bearing an electron-donating OMe group showed the highest activity. Deuterium labeling and control experiments suggested that the dehydrogenation of methanol to generate ruthenium hydride species was the rate-determining step in the reaction. Furthermore, this protocol also provided a ready approach to versatile trideuterated N-methylamines under mild conditions using CD3OD as a deuterated methylating agent.

A Guide for Mono-Selective N-Methylation, N-Ethylation, and N-n-Propylation of Primary Amines, Amides, and Sulfonamides and Their Applicability in Late-Stage Modification

This review provides a comprehensive overview of mono-alkylation methodologies targeting crucial nitrogen moieties - amines, amides, and sulfonamides - found in organic building blocks and pharmaceuticals. Emphasizing the intersection of chemical precision with drug discovery, the central challenge addressed is achieving one-pot mono-selective short-chain N-alkylations (methylations, ethylations, and n-propylations), preventing undesired overalkylation. Additionally, sustainable, safe, and benign alternatives to traditional alkylating agents, including alcohols, carbon dioxide, carboxylic acids, nitriles, alkyl phosphates, quaternary ammonium salts, and alkyl carbonates, are explored. This review, categorized by the nature of the alkylating agent, aids researchers in selecting suitable methods for mono-selective N-alkylation.

Harnessing alcohols as sustainable reagents for late-stage functionalisation: synthesis of drugs and bio-inspired compounds

Alcohol is ubiquitous with unparalleled structural diversity and thus has wide applications as a native functional group in organic synthesis. It is highly prevalent among biomolecules and offers promising opportunities for the development of chemical libraries. Over the last decade, alcohol has been extensively used as an environmentally friendly chemical for numerous organic transformations. In this review, we collectively discuss the utilisation of alcohol from 2015 to 2023 in various organic transformations and their application toward intermediates of drugs, drug derivatives and natural product-like molecules. Notable features discussed are as follows: (i) sustainable approaches for C-X alkylation (X = C, N, or O) including O-phosphorylation of alcohols, (ii) newer strategies using methanol as a methylating reagent, (iii) allylation of alkenes and alkynes including allylic trifluoromethylations, (iv) alkenylation of N-heterocycles, ketones, sulfones, and ylides towards the synthesis of drug-like molecules, (v) cyclisation and annulation to pharmaceutically active molecules, and (vi) coupling of alcohols with aryl halides or triflates, aryl cyanide and olefins to access drug-like molecules. We summarise the synthesis of over 100 drugs via several approaches, where alcohol was used as one of the potential coupling partners. Additionally, a library of molecules consisting over 60 fatty acids or steroid motifs is documented for late-stage functionalisation including the challenges and opportunities for harnessing alcohols as renewable resources.

Hydrogenation of Quinones to Hydroquinones under Atmospheric Pressure Catalyzed by a Metal-Ligand Bifunctional Iridium Catalyst

A general method for the hydrogenation of quinones to hydroquinones under atmospheric pressure has been developed. In the presence of [Cp*Ir(2,2'-bpyO)(H2O)] (0.5-1 mol %), a range of products were obtained in high yields. Furthemore, the expansion of this catalytic system to the hydrogenation of 1,4-benzoquinone diimines was also presented. Functional groups in the bpy ligand were found to be crucial for the catalytic activity of iridium complexes.

Upgrading Ethanol to n-Butanol in the Presence of Carbonate Catalyzed by a Cp*Ir Complex Bearing a Functional 2,2'-Carbonylbibenzimidazole Ligand

Upgrading ethanol to n-butanol as biofuels is an important topic for sustainable chemistry. Herein, a Cp*Ir complex bearing a functional 2,2'-carbonylbibenzimidazole ligand [Cp*Ir(2,2'-COBiBzImH2)Cl][Cl] was designed and synthesized. In the presence of a catalyst (0.1 mol %) and Cs2CO3 (6 mol %), the highest yield of updated n-butanol is up to 37% with 80% selectivity. NH units in the ligand are crucially important for the catalytic activity of the iridium complex.

Hexaazatrinaphthalene-Based Covalent Triazine Framework-Supported Rhodium(III) Complex: A Recyclable Heterogeneous Catalyst for the Reductive Amination of Ketones to Primary Amines

The development of efficient and recyclable heterogeneous catalysts is an important topic. Herein, a rhodium(III) complex Cp*Rh@HATN-CTF was synthesized by the coordinative immobilization of [Cp*RhCl₂]₂ on a hexaazatrinaphthalene-based covalent triazine framework. In the presence of Cp*Rh@HATN-CTF (1 mo l% Rh), a series of primary amines could be obtained via the reductive amination of ketones in high yields. Moreover, catalytic activity of Cp*Rh@HATN-CTF is well maintained during six runs. The present catalytic system was also applied for the large scale preparation of a biologically active compound. It would facilitate the development of CTF-supported transition metal catalysts for sustainable chemistry.

Active Pd Catalyst for the Selective Synthesis of Methylated Amines with Methanol

Selective N-methylation of amines with methanol is an important reaction in the synthesis of high-value-added fine chemicals, including dyes, surfactants, pharmaceuticals, agrochemicals, and materials. However, N-methylated amines possess higher reactivities and are prone to further transform into N,N-dimethylated amines. Therefore, it is still a challenge to controllably regulate the selectivity of N-methylation using heterogeneous catalysts without the use of base. Herein, we developed a series of Pd/Zn(Al)O catalysts with abundant basic sites, and the selectivity of N-methylation was controlled by a heterogeneous Pd/Zn(Al)O catalyst with a Zn/Al ratio of 10 and a Pd loading of 0.4 wt % in the pressure of H₂. The experimental results showed that the appropriate basic properties of the catalyst were beneficial to form the desired N-methylated amine. The low loading of Pd in the catalyst was highly dispersed on the support, providing sufficient active sites. These were attributed to the Zn vacancies formed by Al-doped Zn, which were beneficial to form the highly active and stable Pd sites. Furthermore, a series of amines and nitrobenzenes with different functional groups were well tolerated for the selective synthesis of N-methylated amines in the absence of base.

A bimetallic PdCu–Fe3O4 catalyst with an optimal d-band centre for selective N-methylation of aromatic amines with methanol

Highly efficient and selective N-methylation of aniline with methanol is possible with Pd1Cu0.6–Fe3O4 nanoparticle catalyst.

N-Dimethylation and N-Functionalization of Amines Using Ru Nanoparticle Catalysts and Formaldehyde or Functional Aldehydes as the Carbon Source

N-methylated amines are essential bioactive compounds and have been widely used in the fine and bulk chemical industries, as well as in pharmaceuticals, agrochemicals, and dyes. Developing green, efficient, and low-cost catalysts for methylation of amines by using efficient and easily accessible methylating reagents is highly desired yet remains a significant challenge. Herein, we report the selective N-dimethylation of different functional amines with different functional aldehydes under easy-to-handle and industrially applicable conditions using carbon-supported Ru nanoparticles (Ru/C) as a heterogeneous catalyst. A broad spectrum of amines could be efficiently converted to their corresponding N,N-dimethyl amines with good compatibility of various functional groups. This method is widely applicable to N-dimethylation of primary amines including aromatic, aliphatic amines with formaldehyde, and synthesis of tertiary amines from primary, secondary amines with different functional aldehydes. The advantage of this newly described method includes operational simplicity, high turnover number, the ready availability of the catalyst, and good functional group compatibility. This Ru/C catalyzed N-dimethylation reaction possibly proceeds through a two-step N-methylation reaction process.

Oxidative N-Formylation of Secondary Amines Catalyzed by Reusable Bimetallic AuPd-Fe3O4 Nanoparticles

Bimetallic catalysts are gaining attention due to their characteristics of promoting reactivity and selectivity in catalyzed reactions. Herein, a new catalytic N-formylation of secondary amines using AuPd–Fe₃O₄ at room temperature is reported. Methanol was utilized as the formyl source and 1.0 atm of O₂ gas served as an external oxidant. The bimetallic catalyst, consisting of Au and Pd, makes the reaction more efficient than that using each metal separately. In addition, the catalyst can be effectively recycled owing to the Fe₃O₄ support.

Linear-Organic-Polymer-Supported Iridium Complex as a Recyclable Auto-Tandem Catalyst for the Synthesis of Quinazolinones via Selective Hydration/Acceptorless Dehydrogenative Coupling from o-Aminobenzonitriles

A linear-organic-polymer-supported iridium complex Cp*Ir@P4VP, which is designed and synthesized by the coordinative immobilization of [Cp*IrCl₂]₂ on poly(4-vinylpyridine), was proven to be an efficient heterogeneous autotandem catalyst for synthesizing quinazolinones via selective hydration/acceptorless dehydrogenative coupling from o-aminobenzonitriles. Furthermore, the synthesized catalyst was recycled five times without an obvious decrease in the catalytic activity.

N-Methylation of Amines with Methanol in the Presence of Carbonate Salt Catalyzed by a Metal-Ligand Bifunctional Ruthenium Catalyst [(p-cymene)Ru(2,2'-bpyO)(H2O)]

A ruthenium complex [(p-cymene)Ru(2,2'-bpyO)(H₂O)] was found to be a general and efficient catalyst for the N-methylation of amines with methanol in the presence of carbonate salt. Moreover, a series of sensitive substituents, such as nitro, ester, cyano, and vinyl groups, were tolerated under present conditions. It was confirmed that OH units in the ligand are crucial for the catalytic activity. Notably, this research exhibited the potential of metal-ligand bifunctional ruthenium catalysts for the hydrogen autotransfer process.

Selective synthesis of N-monomethyl amines with primary amines and nitro compounds

The development of the selective N-monomethylation of primary amines and nitro compounds by using various methylating agents, such as MeX, carbon dioxide, methanol, formaldehyde, formic acid and dimethyl carbonate.

Recent advances in sustainable organic transformations using methanol: expanding the scope of hydrogen-borrowing catalysis

Recent progress relating to sustainable approaches using methanol as a C1-alkylating agent for C–Me and N–Me bond formation is discussed.

Selective N-monomethylation of primary anilines with the controllable installation of N-CH2D, N-CHD2, and N-CD3 units

The selective N-monomethylation of primary anilines with the controllable installation of N-CH₂D, N-CHD₂, and N-CD₃ units was realized by using the amine-borane/N,N-dimethylformamide (DMF) system as the methyl precursor.