LongLarf

Publication date: 14 October 2021

Source: Chem, Volume 7, Issue 10

Author(s): Binlin Zhao, Baskaran Prabagar, Zhuangzhi Shi

Supported nanoparticles: This review summarizes recent advances in the development of new support materials or novel supported NPs catalytic systems for functionalization of the challenging C−H bond under heterogeneous conditions. Furthermore, a deep scientific understanding of the mechanisms, active species, role of base and oxidants for these systems are also discussed to gain insight into the advance in the rational design of efficient catalytic systems, which may serve as an inspiration to researchers in their future work.

Abstract

Supported metal nanoparticles (NPs) catalysed chemical transformations have been a vital area of research over the last few decades. Catalysis by supported NPs not only plays a pivotal role in the production of fine chemicals such as coupling products, heterocycles, alcohols, carbonyl compounds, acids, etc. but also provides sustainable chemical processes. The use of supported metal NPs provides a much prosperous basis than conventional homogeneous and heterogeneous catalysts for tuning reactivity, recyclability, high productivity and environment benevolent alternative for C−H functionalization. Consequently, as evidenced in the literature, various support materials such as silica, metal oxides, zeolites, carbon-based materials, bio-materials, magnetic materials, and MOFs have been moderately investigated in order to exploit their benefit in supported metal NPs catalyzed various C−H functionalizations. This review aims to summarize recent advances in the development of new support materials or novel supported NPs catalytic systems for functionalization of the challenging C−H bond under heterogeneous conditions. Furthermore, a deep scientific understanding of the mechanisms, active species, role of base and oxidants for these systems are also discussed to gain insight into the advance in the rational design of efficient catalytic systems, which may serve as an inspiration to researchers in their future work.

Towards sustainable H₂ production: To bring electrocatalytic hydrogen production into the sustainable realm, earth-abundant metal catalysts should function with water as the substrate. These newly reported hydrogen-generating catalysts of Ni^II are robust, stable in air and electrocatalytically reduce water to hydrogen with excellent Faradaic efficiency. Computations supplemented our understanding of a unique ligand-based electron transfer with the cooperativity of the PN³P ligand as an electron reservoir as a requirement for successful catalysis.

Abstract

Water is the most sustainable source for H₂ production, and the efficient electrocatalytic production of H₂ from mixed water/acetonitrile solutions by using two new air-stable nickel(II) pincer complexes, [Ni(κ³-2,6-{Ph₂PNR}₂(NC₅H₃)Br₂] (R=H I, Me II) is reported. Hydrogen generation from H₂O/CH₃CN solutions is initiated at −2 V against Fc^+/0, and bulk electrocatalysis studies showed that the catalyst functions with an excellent Faradaic efficiency and a turnover frequency of 160 s⁻¹. A DFT computational investigation of the reduction behavior of I and II revealed a correlation of H₂ formation with charge donation from electrons originating in a reduced ligand-localized orbital. As a result, these catalysts are proposed to proceed by a novel mechanism involving electron/proton transfer between a Ni^0I species bonded to an anionic PN³P ligand (“L⁻/Ni^0I”) and a Ni^I-hydride (“Ni−H”). Furthermore, these catalysts are able to reduce phenol and acetic acid, more active proton sources, at lower potentials that correlate with the substrate pK _a.

Abstract

An enantioselective phosphine-catalyzed transformation has been developed for the synthesis of chiral cyclobutene triesters and fluorinated spirocyclic compounds. The strategy involved a P(III)/P(V) redox cycling process, via in situ reduction of phosphine oxide with phenylsilane. This catalytic methodology has enabled the enantioselective synthesis of functionalized cyclobutenes (24 examples, up to 94% ee). On the occasion of the extension of this study to α-ketoester indenone substrates, a surprising reactivity has been discovered for the synthesis of spiro-indenone products.

Herein, the first decarboxylative hydroxylation reaction to synthesize phenols from benzoic acids is reported. The method overcomes the challenges associated with conventional decarboxylation of benzoic acids and can be applied even for the late-stage functionalization.

Abstract

Herein, we report the first decarboxylative hydroxylation to synthesize phenols from benzoic acids at 35 °C via photoinduced ligand-to-metal charge transfer (LMCT)-enabled radical decarboxylative carbometalation. The aromatic decarboxylative hydroxylation is synthetically promising due to its mild conditions, broad substrate scope, and late-stage applications.

Mechanochemical ball-milling enabled the direct amidation of esters through simple coupling under basic conditions (see scheme). A wide range of esters underwent amidation by this method with an array of primary and secondary amides without the need for a bulk solvent, catalysts, or additives.

Abstract

The direct mechanochemical amidation of esters by ball milling is described. The operationally simple procedure requires an ester, an amine, and substoichiometric KOtBu and was used to prepare a large and diverse library of 78 amide structures with modest to excellent efficiency. Heteroaromatic and heterocyclic components are specifically shown to be amenable to this mechanochemical protocol. This direct synthesis platform has been applied to the synthesis of active pharmaceutical ingredients (APIs) and agrochemicals as well as the gram-scale synthesis of an active pharmaceutical, all in the absence of a reaction solvent.

Herein, the first decarboxylative hydroxylation reaction to synthesize phenols from benzoic acids is reported. The method overcomes the challenges associated with conventional decarboxylation of benzoic acids and can be applied even for the late-stage functionalization.

Abstract

Herein, we report the first decarboxylative hydroxylation to synthesize phenols from benzoic acids at 35 °C via photoinduced ligand-to-metal charge transfer (LMCT)-enabled radical decarboxylative carbometalation. The aromatic decarboxylative hydroxylation is synthetically promising due to its mild conditions, broad substrate scope, and late-stage applications.

Saturated heterocycles are found in numerous therapeutics and bioactive natural products and are abundant in many medicinal and agrochemical compound libraries. To access new chemical space and function, many methods for functionalization on the periphery of these structures have been developed. Comparatively fewer methods are known for restructuring their core framework. Herein, we describe a visible light–mediated ring contraction of α-acylated saturated heterocycles. This unconventional transformation is orthogonal to traditional ring contractions, challenging the paradigm for diversification of heterocycles including piperidine, morpholine, thiane, tetrahydropyran, and tetrahydroisoquinoline derivatives. The success of this Norrish type II variant rests on reactivity differences between photoreactive ketone groups in specific chemical environments. This strategy was applied to late-stage remodeling of pharmaceutical derivatives, peptides, and sugars.

Synthesis
DOI: 10.1055/a-1549-1082

We report an efficient method for the direct β-acylation of 2-ylideneoxindoles with acyl chlorides that is catalyzed by organophosphanes in the presence of base. A variety of functionalized 2-ylideneoxindoles were prepared in moderate to good yields under mild, metal-free conditions via a tandem phospha-Michael/O-acylation/intramolecular cyclization/rearrangement sequence. Mechanistic investigations revealed that C–O bond cleavage on a possible betaine intermediate is the key step for the installation of the keto-functionality at the β-position of 2-ylideneoxindoles in a highly stereospecific manner. The synthetic utility of this protocol could also be proven by a scale-up reaction and synthetic transformations of the products.
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

Article in Thieme eJournals:
Table of contents  |  Abstract  |  Full text

Synthesis
DOI: 10.1055/a-1577-5947

Carbon dioxide (CO2) is an attractive renewable one-carbon (C1) feedstock in terms of its earth abundance, low cost, and non-toxicity. Developing new catalytic systems to realize the practical insertion of CO2 into organic molecules has been of great importance for ecological economics. In recent years, outstanding improvements have been carried out in the field of light-driven catalytic carboxylation via the activation of CO2 as the key reagent. In this short review, the recent developments of light-promoted carboxylation utilizing CO2 to synthesize value-added chemicals using a dual visible-light photoredox/transition-metal catalyst or a photoredox catalyst are highlighted.1 Introduction2 Visible-Light-Driven Carboxylation Using Transition-Metal Photocatalysts2.1 Transition-Metal-Catalyzed Carboxylation of Alkenes2.2 Transition-Metal-Catalyzed Carboxylation of C(sp2)–X (X = Cl, Br, OTf) Bonds2.3 Transition-Metal-Catalyzed Carboxylation of Alkynes2.4 Transition-Metal-Catalyzed Carboxylation of Carbons Attached to Nitrogen3 Light-Driven Carboxylation via Organo-Photocatalysis3.1 Photocatalytic Carboxylation of Alkenes3.2 Photocatalytic Carboxylation of C(sp3)–H Bonds4 Conclusion
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

Article in Thieme eJournals:
Table of contents  |  Abstract  |  Full text

Complexes, chirality and catalysts: 1,3-P,N hybrid ligands are broadly applied in cooperative catalysis, but show limited electronic variation. We report novel analogues with a high N-basicity, based on 7-membered cyclic imines. Their transition metal complexes demonstrated their donor strength (W), hemilabile coordination (Rh), and catalytic activity for nitrile hydration (Ru) and transfer hydrogenation (Ru, Ir). Chiral derivatives were also obtained, synthesized from l-menthone.

Abstract

Novel seven-membered cyclic imine-based 1,3-P,N ligands were obtained by capturing a Beckmann nitrilium ion intermediate generated in situ from cyclohexanone with benzotriazole, and then displacing it by a secondary phosphane under triflic acid promotion. These “cycloiminophosphanes” possess flexible non-isomerizable tetrahydroazepine rings with a high basicity; this sets them apart from previously reported iminophophanes. The donor strength of the ligands was investigated by using their P-κ¹- and P,N-κ²-tungsten(0) carbonyl complexes, by determining the IR frequency of the trans-CO ligands. Complexes with [RhCp*Cl₂]₂ demonstrated the hemilability of the ligands, giving a dynamic equilibrium of κ¹ and κ² species; treatment with AgOTf gives full conversion to the κ² complex. The potential for catalysis was shown in the Ru^II-catalyzed, solvent-free hydration of benzonitrile and the Ru^II- and Ir^I-catalyzed transfer hydrogenation of cyclohexanone in isopropanol. Finally, to enable access to asymmetric catalysts, chiral cycloiminophosphanes were prepared from l-menthone, as well as their P,N-κ²-Rh^III and a P-κ¹-Ru^II complexes.

A transition-metal-free method using tert-butyl hypoiodite (t-BuOI) or N-iodosuccinimide (NIS) for the intramolecular C−H amination of N-alkylsulfamides is reported. The six-membered cyclic sulfamide products can be easily converted into a variety of useful 1,3-diamines. The present amination that effectively proceeds under ambient conditions, features operationally simple, practical, and scalable methodology.

Abstract

1,3-Diamines are an important class of compounds that are broadly found in natural products and are also widely used as building blocks in organic synthesis. Although the intramolecular C−H amination of N-alkylsulfamide derivatives is a reliable method for the construction of 1,3-diamine structures, the majority of these methods involve the use of a transition-metal catalyst. We herein report on a new transition-metal-free method using tert-butyl hypoiodite (t-BuOI) or N-iodosuccinimide (NIS), enabling secondary non-benzylic and tertiary C−H amination reactions to proceed. The cyclic sulfamide products can be easily transformed into 1,3-diamines. Mechanistic investigations revealed that amination reactions using t-BuOI or NIS each proceed via different pathways.

Abstract

The development of a user-friendly reusable laboratory equipment for the delivery of sensitive reagents and catalysts is described. The tightness of these Teflon Magnetic Stirring Capsules (TMSC) is ensured by the magnetic force and release of the reagent inside the solution is triggered by adjusting the stirring rate so that the centrifuge force exceeds the magnetic force. They can be loaded with several chemicals at the same time and do operate across a broad range of temperatures. The inertness of Teflon facilitates reaction purification.