Aayushi Arora

Anthracene-based ligand L1 comprising an imine functionality and a tellurium (Te) donor moiety has been prepared. This ligand L1 has been characterized using ¹H, ¹³C and ¹²⁵Te NMR spectroscopic techniques. The novel palladium(II) complex 1 and ruthenium(II) complex 2 have been synthesized by reacting organotellurium ligand L1 and Na₂PdCl₄/[Ru p(cymene)Cl₂]₂, respectively. The Pd(II) complex 1 and Ru(II) complex 2 were characterized with high resolution mass spectrometry (HR-MS) and ¹²⁵Te NMR spectra. The molecular structures of complexes 1 and 2 were authenticated with single crystal X-ray diffraction. Both the complexes are thermally stable, robust, and air and moisture insensitive. Palladium complex 1 exhibits nearly square planar geometry. The molecular structure of complex 2 has a pseudo-octahedral half sandwich piano-stool geometry around ruthenium. The catalytic activity of complex 1 has been explored for O-arylation of phenol, whereas the catalytic activity of complex 2 was explored for aldehyde to amide conversion. A variety of structurally different chloroarenes have been coupled with phenol employing 1 as a catalyst. A wide range of aldehydes containing different functional groups (viz. H, –Me, –NO₂, F, OMe, Cl and Br at the para position) were readily converted into their corresponding amide by employing Ru(II) complex 2 as a catalyst in a reaction time of 12 hours.

Suzuki–Miyaura cross-coupling (SMC) is an extremely useful reaction in organic syntheses. During the last two decades, many researchers across the world have employed organochalcogen compounds in various ways for the development of catalytic systems for this reaction. Chalcogen-ligated molecular complexes have been designed using such compounds as ligands, and applied as homogeneous catalytic systems. During the period 2013–2022, various heterogeneous and nano-catalytic systems have also been developed using organosulphur, organoselenium and organotellurium compounds. The main advantages associated with such systems are their easy synthesis and air- and moisture-insensitivity. This article aims to provide insights into the synthetic methodologies pertaining to the preparation of (i) these catalytically relevant and useful compounds and (ii) the heterogeneous and nano-catalytic systems designed using them. Another major focus of the article is to rationalize and critically analyse the effect of chalcogen donor on the size, composition, morphology and shape of the nanostructure. A critical analysis of the applications of all such catalytic systems in Suzuki–Miyaura coupling is presented in detail. Various factors (e.g., temperature) which affect the catalytic performance are also rationalized. The effects of binding mode, ligand framework, chalcogen donor atom and metal are also covered, along with all other factors that influence the catalytic potential of the systems. Various other aspects such as green catalysis (in aqueous medium and in air), and use of non-conventional (ultrasonic radiation) energy sources are analysed. Applications of heterogeneous and nanocatalytic systems apart from Suzuki coupling are also highlighted, and challenges and future scope are elaborated.

Diaryl ethers form an important class of organic compounds. The classic copper-mediated Ullmann diaryl ether synthesis has been known for many years and involves the coupling of phenols with aryl halides. However, the use of high reaction temperature, high catalyst loading and expensive ligands has created a need for the development of alternative catalytic systems. In the recent past, organosulphur and organoselenium compounds have been used as building blocks for developing homogeneous, heterogeneous and nanocatalysts for this C–O coupling reaction. Homogeneous catalytic systems include preformed complexes of metals with organosulphur and organoselenium ligands. The performance of such complexes is influenced dramatically by the nature of the chalcogen (S or Se) donor site of the ligand. Nanocatalytic systems (including Pd₁₇Se₁₅, Pd₁₆S₇ and Cu_1.8S) have been designed using a single-source precursor route. Heterogeneous catalytic systems contain either metal (Cu or Pd) or metal chalcogenides (Pd₁₇Se₁₅ or Cu_1.8S) as catalytically active species. This article aims to cover the simple and straightforward methodologies and approaches that are adopted for developing catalytically relevant organosulfur and organoselenium ligands, their homogeneous metal complexes, heterogeneous and nanocatalysts. The effects of chalcogen (S or Se) donor, halogen (Cl/Br/I) of aryl halide, nature (electron withdrawing or electron donating) of substituents present on the aromatic ring of aryl halides or substituted phenols and position (ortho or para) of substitution on the results of catalytic reactions have been critically analyzed and summarized. The effect of composition (Pd₁₇Se₁₅ or Pd₁₆S₇) on the performance of nanocatalytic systems is also highlighted. Substrate scope has also been discussed in all three types of catalysis. The superiority of heterogeneous catalytic systems (e.g., Pd₁₇Se₁₅ immobilised on graphene oxide) indicates the bright future possibilities for the development of efficient catalytic systems using similar or tailored ligands for this reaction.

The first report of Pd₆P nanospheres synthesized via a single-source precursor route, further immobilized over graphene oxide sheets and explored for applications in electrochemical hydrogen evolution reaction.

Herein, we report a promising graphene oxide (GO) anchored robust and thermally stable heterogeneous catalytic system containing the low cost and less toxic copper oxide as a catalytically active material for C–O coupling reactions. A hybrid ligand (i.e. PPh₂–CH₂–CH₂–NH₂) has been used for the first time for functionalization of the GO surface. This ligand grafted over GO sheets via covalent linkages acts as an efficient stabilizing and chelating agent for CuO nanoparticles through P and N donor sites to form the catalytic system (GO–PN–CuO). The powder X-ray diffraction (PXRD), infrared (IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), Brunauer–Emmett–Teller (BET) studies, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM) and Raman spectroscopy confirmed the step-wise formation of GO–PN–CuO. The catalytic potential of GO–PN–CuO has been explored for the C–O coupling reactions of phenols with several aryl bromides and chlorides under mild reaction conditions. The covalent linkage of the hybrid ligand with GO sheets and the strong binding abilities of P, N donor sites with CuO render high stability to GO–PN–CuO. As a result, the catalytic system offers the advantage of recyclability up to five reaction cycles without any considerable loss in activity.

During the last two decades, several research groups across the globe have utilized organochalcogen compounds as: (i) ligands for developing homogeneous, i.e. chalcogen-ligated metal complexes, and heterogeneous catalytic systems; (ii) stabilizers for developing metal nanocatalytic systems (iii) building blocks of single-source precursors for nanosized metal chalcogenides. The electron-donating abilities of chalcogen (S, Se, and Te) donors make them promising in the field of phosphine-free catalysis. Generally, such ligands and catalytic systems are easily synthesizable. In the preceding decade (2011–2020), a variety of homogeneous, heterogeneous, and nanocatalytic systems have been developed using organosulfur, organoselenium, and organotellurium ligands. Such catalytic systems have been extensively used for the Heck coupling reaction. This perspective article covers the synthetic methodologies used for such ligands and catalytic systems designed during 2012–2020. Another major focus of this article is the catalysis of Heck coupling with such systems. The substrate scope, green catalysis, use of conventional and non-conventional sources of energy, and catalytic performances are analysed and covered. The effects of the operational parameters of reactions have also been discussed. Various factors that influence the catalytic efficiencies have been highlighted, and the variations in the catalytic efficiencies of different catalytic systems have been critically analysed. The behaviours of the catalytic systems during the reactions have been summarized and correlated with mechanistic pathways. The catalytic cycles proposed for this reaction have also been paid sufficient attention.

Organoselenium ligands have attracted great attention among researchers during the past two decades. Various homogeneous, heterogeneous and nanocatalytic systems have been designed using such ligands. Although reports on selenium ligated homogeneous catalysts are quite high in number, significant work has also been done on the development of heterogeneous and nanocatalytic systems using organoselenium ligands. A review article, focusing on the utility of organoselenium compounds in the development of catalytic systems, was published in 2012 (A. Kumar, G. K. Rao, F. Saleem and A. K. Singh, Dalton Trans., 2012, 41, 11949). Moreover, it mainly covered the homogeneous catalysts. There are no review articles in the literature on heterogeneous and nanocatalytic systems designed using organoselenium compounds and their applications. Hence, this perspective aims to cover the developments pertaining to the synthetic aspects of such catalytic systems (using organoselenium compounds) and their applications in catalysis of a variety of chemical transformations. Salient features and advantages of organoselenium compounds have also been highlighted to justify the rationale behind their use in catalyst development. Their performance in various chemical transformations [viz. Suzuki–Miyaura coupling, Heck coupling, Sonogashira coupling, O-arylation of phenol, transfer hydrogenation of aldehydes and ketones, aldehyde–alkyne–amine (A³) coupling, hydration of nitriles, conversion of aldehydes to amides, cross-dehydrogenative coupling (CDC), photodegradation of substrates (formic acid, methylene blue), reduction of nitrophenols, electrolysis (hydrogen evolution reaction and oxygen reduction reactions), organocatalysis and dye sensitized solar cells] and relevant aspects of catalytic processes (such as recyclability, substrate scope and green aspects) have been critically analyzed. Future perspectives have also been discussed.

First precursor-architecture controlled synthesis of Pd ₉ Te ₄ and PdTe nanostructures that have potential applications in Suzuki coupling of 4-chlorobenzaldehyde and catalytic reduction of 4-nitrophenol.