Iron-catalyzed reduction of aromatic aldehydes with paraformaldehyde and H2O as the hydrogen source

Nickel-Catalyzed Reductive Alkyne Hydrocyanation Enabled by Malononitrile and a Formaldehyde Additive

The development of a nickel-catalyzed reductive alkyne hydrocyanation is described using 2-methyl-2-phenylmalononitrile (MPMN), a C-bound electrophilic transnitrilation reagent. Reproducibility issues led to the detection of oxidized hemiaminal impurities within N,N-dimethylacetamide. These impurities release formaldehyde in situ, which was ultimately identified as a critical reaction additive. A range of diaryl and aryl-alkyl alkynes underwent hydrocyanation. Mechanistic experiments revealed that formaldehyde and MPMN undergo a Ni-catalyzed reductive coupling of two π-components, leading to the controlled release of glycolonitrile as the active cyanating agent.

Lignin Residue-Derived Carbon-Supported Nanoscale Iron Catalyst for the Selective Hydrogenation of Nitroarenes and Aromatic Aldehydes

Heterogeneous iron-based catalysts governing selectivity for the reduction of nitroarenes and aldehydes have received tremendous attention in the arena of catalysis, but relatively less success has been achieved. Herein, we report a green strategy for the facile synthesis of a lignin residue-derived carbon-supported magnetic iron (γ-Fe₂O₃/LRC-700) nanocatalyst. This active nanocatalyst exhibits excellent activity and selectivity for the hydrogenation of nitroarenes to anilines, including pharmaceuticals (e.g., flutamide and nimesulide). Challenging and reducible functionalities such as halogens (e.g., chloro, iodo, and fluoro) and ketone, ester, and amide groups were tolerated. Moreover, biomass-derived aldehyde (e.g., furfural) and other aromatic aldehydes were also effective for the hydrogenation process, often useful in biomedical sciences and other important areas. Before and after the reaction, the γ-Fe₂O₃/LRC-700 nanocatalyst was thoroughly characterized by X-ray diffraction (XRD), N₂ adsorption-desorption, X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HR-TEM), Raman spectroscopy, and thermogravimetric analysis (TGA). Additionally, the γ-Fe₂O₃/LRC-700 nanocatalyst is stable and easily separated using an external magnet and recycled up to five cycles with no substantial drop in the activity. Eventually, sustainable and green credentials for the hydrogenation reactions of 4-nitrobenzamide to 4-aminobenzamide and benzaldehyde to benzyl alcohol were assessed with the help of the CHEM21 green metrics toolkit.

(Cyclopentadienone)iron Complexes: Synthesis, Mechanism and Applications in Organic Synthesis

(Cyclopentadienone)iron tricarbonyl complexes are catalytically active, inexpensive, easily accessible and air-stable that are extensively studied as an active pre-catalyst in homogeneous catalysis. Its versatile catalytic activity arises exclusively due to the presence of a non-innocent ligand, which can trigger its unique redox properties effectively. These complexes have been employed widely in (transfer)hydrogenation (e. g., reduction of polar multiple bonds, Oppenauer-type oxidation of alcohols), C-C and C-N bond formation (e. g., reductive aminations, α-alkylation of ketones) and other synthetic transformations. In this review, we discuss the remarkable advancement of its various synthetic applications along with synthesis and mechanistic studies, until February 2021.

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.

Strategies and mechanisms of metal–ligand cooperativity in first-row transition metal complex catalysts

The use of metal–ligand cooperation (MLC) by transition metal bifunctional catalysts has emerged at the forefront of homogeneous catalysis science.

Base-controlled divergent synthesis of vinyl sulfones from (benzylsulfonyl)benzenes and paraformaldehyde

A tuneable metal-free protocol for the selective preparation of α-substituted vinyl sulfone and (E)-vinyl sulfone derivatives has been described. The base played an important role in the selectivity control of transformation.

Synthesis and Catalytic Application of Knölker-Type Iron Complexes with a Novel Asymmetric Cyclopentadienone Ligand Design

Asymmetric catalysis is an essential tool in modern chemistry, but increasing environmental concerns demand the development of new catalysts based on cheap, abundant, and less toxic iron. As a result, Knölker-type catalysts have emerged as a promising class of iron catalysts for various chemical transformations, notably the hydrogenation of carbonyls and imines, while asymmetric versions are still under exploration to achieve optimal enantio-selectivities. In this work, we report a novel asymmetric design of a Knölker-type catalyst, in which the C2-rotational symmetric cyclopentadienone ligand possesses chiral substituents on the 2- and 5-positions near the active site. Four examples of the highly modular catalyst design were synthesized via standard organic procedures, and their structures were confirmed with NMR, IR, MS, and polarimetry analysis. Density functional theory (DFT) calculations were conducted to elucidate the spatial conformation of the catalysts, and therewith to rationalize the influence of structural alterations. Transfer- and H2-mediated hydrogenations were successfully established, leading to appreciable enantiomeric excesses (ee) values up to 70%. Amongst all reported Knölker-type catalysts, our catalyst design achieves one of the highest ee values for hydrogenation of acetophenone and related compounds.

Direct Sulfoxidation of Aromatic Methyl Thioethers with Aryl Halides by Copper-Catalyzed C(sp3)–H Bond Activation

A copper-catalyzed direct sulfoxidation reaction by C(sp3)–H bond activation has been developed. Starting from sample aromatic methyl thioethers with aryl halides, versatile biologically-active arylbenzylsulfoxide derivatives were efficiently synthesized in good to high yields under mild conditions. This new methodology provides an economical approach toward C(sp3)–C(sp2) bond formation.

Concise synthesis of N-thiomethyl benzoimidazoles through base-promoted sequential multicomponent assembly

An efficient method for the synthesis of N-thiomethyl benzimidazoles from o-phenylenediamines, thiophenols, and aldehydes via C–N/C–S bond formation under metal-free conditions is described. A broad range of functional groups attached to the substrates were well tolerated in this reaction system. Stable and low-toxicity paraformaldehyde was used as the carbon source.

An efficient method for the synthesis of N-thiomethyl benzimidazoles from o-phenylenediamines, thiophenols, and aldehydes via C–N/C–S bond formation under metal-free conditions is described.

Synthesis and applications to catalysis of novel cyclopentadienone iron tricarbonyl complexes

New approaches to enantiomerically-pure cyclopentadienone iron complexes, and their applications to ketone reductions reactions, are described.

Harnessing the Power of the Water-Gas Shift Reaction for Organic Synthesis

Since its original discovery over a century ago, the water-gas shift reaction (WGSR) has played a crucial role in industrial chemistry, providing a source of H2 to feed fundamental industrial transformations such as the Haber-Bosch synthesis of ammonia. Although the production of hydrogen remains nowadays the major application of the WGSR, the advent of homogeneous catalysis in the 1970s marked the beginning of a synergy between WGSR and organic chemistry. Thus, the reducing power provided by the CO/H2 O couple has been exploited in the synthesis of fine chemicals; not only hydrogenation-type reactions, but also catalytic processes that require a reductive step for the turnover of the catalytic cycle. Despite the potential and unique features of the WGSR, its applications in organic synthesis remain largely underdeveloped. The topic will be critically reviewed herein, with the expectation that an increased awareness may stimulate new, creative work in the area.

Eco-friendly hydrogenation of aromatic aldehyde compounds by tandem dehydrogenation of dimethylamine-borane in the presence of a reduced graphene oxide furnished platinum nanocatalyst

An easy and effective synthetic method has been developed for the reduction of aldehyde compounds in the presence of monodisperse Pt(0)/TPA@rGO NPs as the catalyst.

Iron cyclopentadienone complexes derived from C2-symmetric bis-propargylic alcohols; preparation and applications to catalysis

The following complexes were prepared through cyclisation of a bis-propargylic alcohol and were tested as redox catalysts for hydrogen transfer reactions of alcohols and ketones.