Selective N-monoalkylation of aromatic amines with benzylic alcohols by a hydrogen autotransfer process catalyzed by unmodified magnetite

Borrowing Hydrogen for Organic Synthesis

Borrowing hydrogen is a process that is used to diversify the synthetic utility of commodity alcohols. A catalyst first oxidizes an alcohol by removing hydrogen to form a reactive carbonyl compound. This intermediate can undergo a diverse range of subsequent transformations before the catalyst returns the "borrowed" hydrogen to liberate the product and regenerate the catalyst. In this way, alcohols may be used as alkylating agents whereby the sole byproduct of this one-pot reaction is water. In recent decades, significant advances have been made in this area, demonstrating many effective methods to access valuable products. This outlook highlights the diversity of metal and biocatalysts that are available for this approach, as well as the various transformations that can be performed, focusing on a selection of the most significant and recent advances. By succinctly describing and conveying the versatility of borrowing hydrogen chemistry, we anticipate its uptake will increase across a wider scientific audience, expanding opportunities for further development.

Organic synthesis with the most abundant transition metal–iron: from rust to multitasking catalysts

The promising aspects of iron in synthetic chemistry are being explored for three-four decades as a green and eco-friendly alternative to late transition metals. This present review unveils these rich iron-chemistry towards different transformations.

Potassium tert-butoxide mediated C-C, C-N, C-O and C-S bond forming reactions

Potassium tertiary butoxide (KO^tBu) mediated constructions of C-C, C-O, C-N, and C-S bonds are reviewed with special emphasis on their synthetic applications. KO^tBu can be used to perform reactions already known to be carried out using transition metals, but it has advantages in terms of environmental congruence and economic cost. KO^tBu is widely employed in organic synthesis to mediate the construction of C-C, C-O, C-N, C-S and miscellaneous bonds in good to excellent yields. Synthetic uses of KO^tBu in coupling, alkylation, arylation, α-phenylation, cyclization, Heck-type, annulation, photo-arylation, aromatic-substitution, amidation, and silylation reactions are summarized and discussed. The mechanisms through which KO^tBu carries out a specific reaction are also discussed. One of the goals of this review is to attract the attention of chemists as to the benefits of using KO^tBu as an environmentally benign alternative to transition metals and its applications in the construction of chemical bonds with predominant importance in organic synthesis. This review completely covers the synthetic protocols that have been performed using KO^tBu in the last two decades.

Asymmetric Induction with a Chiral Amine Catalyzed by a Ru-PNP Pincer Complex: Insight from Theoretical Investigation

In this paper, the mechanism of asymmetric amination of a racemic alcohol with Ellman's sulfinamide and the origin of diastereoselectivity catalyzed by a Ru-PNP pincer complex were studied using density functional theory (DFT). The mechanism involves dehydrogenation of the racemic alcohol, C-N coupling, and hydrogen transfer from the catalyst to the in situ formed imine. The calculated results indicate that both the alcohol dehydrogenation and imine hydrogenation are stepwise. The hydride transfer from a Ru hydride complex to the imine is shown to be the chirality-determining step in the whole catalytic cycle. It was found that the diastereoselectivity mainly stems from the hydrogen bonding interactions between the oxygen atom of the sulfinyl moiety and the hydrogen atom of the NH group of the ligand.

Fe-Containing MOFs as Seeds for the Preparation of Highly Active Fe/Al-SBA-15 Catalysts in the NAlkylation of Aniline

We have successfully incorporated iron species into mesoporous aluminosilicates (Al-SBA-15) using a simple mechanochemical milling method. The catalysts were characterized by nitrogen physisorption, inductively coupled plasma mass spectrometry (ICP-MS), pyridine (PY) and 2,6-dimethylpyridine (DMPY) pulse chromatography titration, powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX). The catalysts were tested in the N-alkylation reaction of aniline with benzyl alcohol for imine production. According to the results, the iron sources, acidity of catalyst and reaction conditions were important factors influencing the reaction. The catalyst showed excellent catalytic performance, achieving 97% of aniline conversion and 96% of imine selectivity under optimized conditions.

Self-Suspended Nanoparticles for N-Alkylation Reactions: A New Concept for Catalysis

The catalytic activity of snowman-like and core-shell Fe3O4/Au nanoparticles (NPs), obtained through a "wet chemistry" approach which directly restitutes nanocatalysts stable and highly active in the reaction medium, was tested towards N-alkylation reactions. The nanocatalysts were tested for the synthesis of secondary amines. The core-shell NPs, thanks to the surface properties, homogeneous dispersion and intimate connection with reagents in the catalyst medium, exhibited an excellent catalytic activity (e. g. >99 % yield and conversion of aniline in very short time and mild conditions). Owing to the magnetic part, the nanoparticles can be easily separated and reused, showing an almost stable activity after 10 cycles.

Evaluation of heterogeneous catalytic ozonation process for diclofenac degradation in solutions synthetically prepared

Sodium diclofenac (DCF) is a common analgesic and anti-inflammatory drug, which has become an environmental problem due to its growth and accumulation into water bodies. In this work, commercial (with excipients) and analytical (pure) DCF mineralization was studied by means of heterogeneous catalytic ozonation. The process was carried out with magnetite (Fe₃O₄) as a catalyst, which preserves its physical and chemical properties during the process. The best results of mineralization were obtained after a 40-min treatment of 35 mg/L analytical DCF solution, with a 0.5 g/L catalyst concentration. These results showed the highest organic load decrease, measured as dissolved organic carbon (DOC) and chemical oxygen demand (COD), with 94 and 89%, respectively. In addition, the percentage of organic load decrease was compared between the conventional and the catalyzed process. Besides, reaction products were identified by gas chromatography-mass spectrometry (GC-MS) and the catalytic properties were identified by Mössbauer spectroscopy, which showed the catalyst maintained its nature after the process. Finally, the results obtained show that the heterogeneous catalytic process could be an efficient degradation treatment for emerging contaminants such as DCF.

Iron-catalyzed dehydrogenation reactions and their applications in sustainable energy and catalysis

This review article describes recent developments of iron-based acceptorless dehydrogenation (AD) reactions of fundamentally important feedstock, as a route to sustainable chemical synthesis and energy storage applications.

Pd@[nBu₄][Br] as a Simple Catalytic System for N-Alkylation Reactions with Alcohols

Palladium nanoparticles, simply and briefly generated in commercial and cheap onium salts using supercritical carbon dioxide, have been found to be an effective catalytic system for additive free N-alkylation reaction using alcohols via cascade oxidation/condensation/reduction steps.

A Step into an eco-Compatible Future: Iron- and Cobalt-catalyzed Borrowing Hydrogen Transformation

Living on borrowed hydrogen: Recent developments in iron- and cobalt-catalyzed borrowing hydrogen have shown that economically reliable catalysts can be used in this type of waste-free reactions. By using well-defined inexpensive catalysts, known reactions can now be run efficiently without the necessary use of noble metals; however, in addition new types of reactivity can also be discovered.

Carbon-catalysed reductive hydrogen atom transfer reactions

Generally, transition metal catalysts are essential for the reductive hydrogen atom transfer reaction, which is also known as the transfer hydrogenation reaction or the borrowing-hydrogen reaction. It has been reported that graphene can be an active catalyst in ethylene and nitrobenzene reductions, but no report has described carbon-based materials as catalysts for alcohol amination via the borrowing-hydrogen reaction mechanism. Here we show the results from the preparation, characterization and catalytic performance investigation of carbon catalysts in transition metal-free borrowing-hydrogen reactions using alcohol amination and nitro compound/ketone reduction as model reactions. XPS, XRD, SEM, FT-IR and N2 adsorption-desorption studies revealed that C=O group in the carbon catalysts may be a possible catalytically active site, and high surface area is important for gaining high activity. The activity of the carbon catalyst remained unchanged after reuse. This study provides an attractive and useful methodology for a wider range of applications.

Benzimidazolin-2-ylidene N-heterocyclic carbene complexes of ruthenium as a simple catalyst for the N-alkylation of amines using alcohols and diols

Simple non-chelating ruthenium benzimidazolin-2-ylidene complexes as efficient N-alkylation catalysts using alcohols and diols following a hydrogen borrowing strategy.

An efficient heterogenized palladium catalyst for N-alkylation of amines and α-alkylation of ketones using alcohols

Silica supported palladium–NiXantphos complex is an efficient and high turnover heterogeneous catalyst for N-alkylation of amines and α-alkylation of ketones using alcohols under neat conditions at 120–140 °C following hydrogen borrowing strategy.

Heterogeneous catalysis for the direct synthesis of chemicals by borrowing hydrogen methodology

This review summarizes the recent examples of hydrogen transfer-type reactions using supported transition metal catalysts with special emphasis on the one-pot synthesis of chemicals by borrowing hydrogen methodology.

Room temperature N-alkylation of amines with alcohols under UV irradiation catalyzed by Cu–Mo/TiO2

Cu–Mo/TiO₂ can be an active photocatalyst for N-alkylation of amines with alcohols under UV irradiation at room temperature without the addition of noble metals.

A conjugated ketone as a catalyst in alcohol amination reactions under transition-metal and hetero-atom free conditions

A molecular-defined conjugated ketone can be an active catalyst for alcohol amination reactions with up to 98% isolated yields for the desired products.