Stable and Reusable Binaphthyl‐Supported Palladium Catalyst for Aminocarbonylation of Aryl Iodides

A binaphthyl‐supported Pd nanoparticles (Pd‐BNP)‐catalyzed aminocarbonylation of aryl iodides in the presence of carbon monoxide and amines for the synthesis of amides has been developed. This methodology provides an efficient route for the synthesis of a COX‐2 enzyme inhibitor having anti‐inflammatory activity.

     

Magnetic Nanoparticles‐Supported Palladium: A Highly Efficient and Reusable Catalyst for the Suzuki,Sonogashira, and Heck Reactions

A highly efficient, air‐ and moisture‐stable and easily recoverable magnetic nanoparticle‐supported palladium catalyst has been developed for the Suzuki, Sonogashira and Heck reactions. A wide range of substrates was coupled successfully under aerobic conditions. In particular, the performance of the magnetic separation of the catalyst was very efficient, and it is possible to recover and reuse it at least eight times without significant loss of its catalytic activity.     

Zn-Catalyzed Regioselective and Chemoselective Reduction of Aldehydes,Ketones and Imines

An operationally convenient Zn-catalyzed synthesis of alcohols by the reduction of aldehydes, ketones, and α,β-unsaturated aldehydes/ketones is reported. It is a rare example of using mild and sustainable HBpin as a reductant for catalytic reduction of carbonyl compounds in the absence of acid or base as hydrolysis reagent. The reaction is upscalable and proceeds in high selectivity without the formation of boronate ester by-products, and tolerates sensitive functionalities, such as iodo, bromo, chloro, fluoro, nitro, trifluoromethyl, aminomethyl, alkynyl, and amide. The Zn(OAc)₂/HBpin combination has been also proved to be chemoselective for the C=N reduction of imine analogs.     

An Efficient Catalytic Aerobic Oxidation of Alcohols in Water Using Hypervalent Iodine(V)

A transition metal‐free aerobic oxidation of alcohols to the corresponding aldehydes or ketones can be effectively catalysed by iodoxybenzene (PhIO₂)/Br₂/NaNO₂ in water.     

Palladium‐Catalyzed Reduction of Carboxylic Acids to Aldehydes with Hydrosilanes in the Presence of Pivalic Anhydride

A palladium catalyst system that allows the reduction of carboxylic acids to the corresponding aldehydes with hydrosilanes as reducing agent and pivalic anhydride as an indispensable reagent has been developed. A simple mixture of commercially available bis(dibenzylideneacetone)palladium(0) [Pd(dba)₂], tri(para‐tolyl)phosphane and methylphenylsilane realized the reduction of various aliphatic carboxylic acids as well as benzoic acids to aldehydes in good to high yields.

     

Nanocrystalline Magnesium Oxide‐Stabilized Palladium(0): An Efficient and Reusable Catalyst for Selective Reduction of Nitro Compounds

An efficient, mild and selective synthesis of aromatic and aliphatic amines from the corresponding nitro compounds has been realized by using a ligand‐free heterogeneous nanocrystalline magnesium oxide‐stabilized palladium(0) catalyst, employing molecular hydrogen as the reductant. The catalyst is recovered quantitatively by simple filtration and was reused for several cycles with consistent activity.     

Nanocrystalline Magnesium Oxide Stabilized Palladium(0): An Efficient Reusable Catalyst for Room Temperature Selective Aerobic Oxidation of Alcohols

Nanocrystalline magnesium oxide‐stabilized palladium(0) [NAP‐Mg‐Pd(0)], as an efficient catalytic system has been employed for the selective oxidation of alcohols using atmospheric oxygen as a green oxidant at room temperature. Various alcohols could be transformed into their corresponding aldehydes or ketones in good to excellent yields using a set of optimal conditions. NanoActive™ Magnesium Oxide Plus, [NAP‐MgO] with its three‐dimensional structure and well‐defined shape acts as an excellent support for well dispersed palladium(0) nanoparticles. This catalyst can be recovered and reused for several cycles without any significant loss of catalytic activity.     

Palladium Nanoparticles Immobilized on Nano‐Silica Triazine Dendritic Polymer (Pdnp‐nSTDP): An Efficient and Reusable Catalyst for Suzuki–Miyaura Cross‐Coupling and Heck Reactions

A new catalyst based on palladium nanoparticles immobilized on nano‐silica triazine dendritic polymer (Pd_np‐nSTDP) was synthesized and characterized by FT‐IR spectroscopy, thermogravimetric analysis, field emission scanning electron microscopy, energy dispersive X‐ray, transmission electron microscopy and elemental analysis. The size of the palladium nanoparticles was determined to be 3.1±0.5 nm. This catalytic system showed high activity in the Suzuki–Miyaura cross‐coupling of aryl iodides, bromides and chlorides with arylboronic acids and also in the Heck reaction of these aryl halides with styrenes. These reactions were best performed in a dimethylformamide (DMF)/water mixture (1:3) in the presence of only 0.006 mol% and 0.01 mol% of the catalyst, respectively, under conventional conditions and microwave irradiation to afford the desired coupling products in high yields. The Pd_np‐nSTDP was also used as an efficient catalyst for the preparation of a series of star‐ and banana‐shaped compounds with a benzene, pyridine, pyrimidine or 1,3,5‐triazine unit as the central core. Moreover, the catalyst could be recovered easily and reused several times without any considerable loss of its catalytic activity.     

Development of Molecular Sieves‐Supported Palladium Catalyst and Chemoselective Hydrogenation of Unsaturated Bonds in the Presence of Nitro Groups

The chemoselective hydrogenation of unsaturated bonds and azide functionalities is achieved in the presence of nitro groups by a heterogeneous palladium catalyst supported on molecular sieves (MS3A). The present method shows a wide‐range of applicability with regard to substrates and the catalyst can be easily prepared and reused at least three times without any loss of activity.     

Palladium on Carbon: An Efficient,Heterogeneous and Reusable Catalytic System for Carbonylative Synthesis of N‐Substituted Phthalimides

The application of palladium on carbon (Pd/C) as a heterogeneous recyclable catalyst was investigated for the double carbonylation of o‐dihaloarenes with amines providing excellent yield of N‐substituted phthalimides in shorter reaction time as compared to earlier reported homogeneous protocols. Furthermore, the scope of the developed protocol was applied for the synthesis N‐substituted phthalimides from o‐halobenzoates and o‐halobenzoic acid via a single step carbonylative cyclization reaction. The developed methodology describes an efficient one‐step approach for the synthesis of an important class of heterocycles and tolerates a wide variety of functional groups. It circumvents the use of phosphine ligands with an additional advantage of catalyst recyclability for up to eight consecutive cycles.     

Potassium Phosphate‐Catalyzed Chemoselective Reduction of α‐Keto Amides: Route to Synthesize Passerini Adducts and 3‐Phenyloxindoles

A chemoselective reduction of α‐keto amides to biologically important α‐hydroxy amides (mandelamides) by polymethylhydrosiloxane (PMHS) using 5 mol% potassium phosphate (K₃PO₄) as catalyst has been developed. This transition metal‐free protocol discloses excellent chemoselectivity for the ketone reduction of α‐keto amides in the presence of other reducible functionalities like ketone, nitro, halides, nitrile and amide. Also, the chemoselectively reduced α‐hydroxy amide has been derivatized to isocyanide‐free Passerini adducts. The N‐alkyl‐α‐hydroxy amides have been successfully converted to 3‐phenyloxindole derivatives by treatment with methanesulfonyl cholride and triethylamine.

     

Reusable,Polymer‐Supported,Palladium‐Catalyzed,Atom‐ Efficient Coupling Reaction of Aryl Halides with Sodium Tetraphenylborate in Water by Focused Microwave Irradiation

A rapid and efficient cross‐coupling reaction of sodium tetraphenylborate with aryl bromides was carried out in water at 120 °C in the presence of a polymer‐supported palladium catalyst and potassium carbonate under focused microwave irradiation. All four phenyl groups of sodium tetraphenylborate participated in the reaction and produced polyfunctional biaryls in excellent yields. The polymeric catalyst can be easily separated from the reaction mixture and reused more than 10 times without showing any decrease in activity.     

Nanocrystalline Magnesium Oxide‐Stabilized Palladium(0): An Efficient and Reusable Catalyst for Suzuki and Stille Cross‐Coupling of Aryl Halides

A nanocrystalline magnesium oxide‐stabilized palladium(0) catalyst is prepared by counterion stabilization of PdCl₄²⁻ with nanocrystalline MgO followed by reduction. This ligand‐free heterogeneous nanocrystalline MgO‐stabilized nanopalladium [NAP Mg Pd(0)] catalyst using the basic MgO in place of basic ligands exhibits excellent activity in Suzuki and Stille cross‐coupling of haloarenes (chloro, bromo and iodo) to afford the unsymmetrical biaryls. The catalyst is quantitatively recovered by simple filtration and reused for four cycles with almost consistent activity.     

Palladium Nanoparticles on Thermoresponsive Hydrogels and their Application as Recyclable Suzuki–Miyaura Coupling Reaction Catalysts in Water

Palladium nanoparticles were immobilized on PNIPAM:4‐VP hydrogels. The resultant püalladium catalysts showed high activities for Suzuki–Miyaura coupling reactions in water. The recyclability of the catalysts was improved by using 4‐VP as a co‐monomer in the hydrogels due to reduced Pd leaching during the reactions.     

Hydrophilic CNC‐Pincer Palladium Complexes: A Source for Highly Efficient,Recyclable Homogeneous Catalysts in Suzuki–Miyaura Cross‐Coupling

The Suzuki biaryl coupling of a range of electronically dissimilar arylboronic acids and aryl bromides is performed in neat water with excellent to quantitative yields by means of a new CNC‐pincer palladium catalyst that is soluble in water due to its para‐carboxy group. Extremely high turnover numbers and frequencies combined with a remarkable robustness allow an effective catalyst reuse in sustainable conditions.     

Efficient Palladium‐Catalyzed Double Arylation of Phosphonoalkynes and Diarylalkynes in Water: Use of a Dinuclear Palladium(I) Catalyst

A novel use of the dinuclear palladium(I) catalyst [(OCH₂CMe₂CH₂O)P‐S‐Pd(PPh₃)]₂ in aqueous medium for the double arylation of phosphonoalkynes as well as diarylalkynes is reported. This double arylation requires both the iodoarene and arylboronic acid along with the catalyst. The structures of some key products have been proven by X‐ray crystallography.     

Efficient Hydrogenation of Nitrogen Heterocycles Catalyzed by Carbon‐Metal Covalent Bonds‐Stabilized Palladium Nanoparticles: Synergistic Effects of Particle Size and Water

We reveal here the first hydrogenation of nitrogen heterocycles catalyzed by carbon–metal covalent bonds‐stabilized palladium nanoparticles in water under mild conditions. Using a one‐phase reduction method, smaller metal–carbon covalent bond‐stabilized Pd nanoparticles were prepared with a size distribution of 2.5±0.5 nm, which showed extraordinary synergistic effects with water in the catalytic hydrogenation of nitrogen heterocycles. Water was supposed to accelerate substrate absorption and synergistic activation of molecular hydrogen on the Pd nanoparticles surface. The nanosized Pd catalyst could be easily recovered and reused for 5 runs.

     

Rhodium‐Catalysed Coupling of Allylic,Homoallylic, and Bishomoallylic Alcohols with Aldehydes and N‐Tosylimines: Insights into the Mechanism

The isomerisation of alkenols followed by reaction with aldehydes or N‐tosylimines catalysed by rhodium complexes has been studied. The catalytically active rhodium complex is formed in situ from commercially available (cyclooctadiene)rhodium(I) chloride dimer [Rh(COD)Cl]₂. The tandem process affords aldol and Mannich‐type products in excellent yields. The key to the success of the coupling reaction is the activation of the catalysts by reaction with postassium tert‐butoxide (t‐BuOK), which promotes a catalytic cycle via alkoxides rather than rhodium hydrides. This mechanism minimises the formation of unwanted by‐products. The mechanism has been studied by ¹H NMR spectroscopy and deuterium labelling experiments.     

TEMPO and Carboxylic Acid Functionalized Imidazolium Salts/Sodium Nitrite: An Efficient,Reusable, Transition Metal‐Free Catalytic System for Aerobic Oxidation of Alcohols

An effective catalytic system comprising a 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO) functionalized imidazolium salt ([Imim‐TEMPO]⁺ X⁻), a carboxylic acid substituted imidazolium salt ([Imim‐COOH]⁺ X⁻), and sodium nitrite (NaNO₂) was developed for the aerobic oxidation of aliphatic, allylic, heterocyclic and benzylic alcohols to the respective carbonyl compounds with excellent selectivity up to >99%, even at ambient conditions. Notably, the catalyst system could preferentially oxidize a primary alcohol to the aldehyde rather than a secondary alcohol to the ketone. Moreover, the reaction rate is greatly enhanced when a proper amount of water is present. And a high turnover number (TON 5000) is achieved in the present transition metal‐free aerobic catalytic system. Additionally, the functionalized imidazolium salts are successfully reused at least four times. This process thus represents a greener pathway for the aerobic oxidation of alcohols into carbonyl compounds by using the present task‐specific ionic liquids in place of the toxic and volatile additive, such as hydrogen bromide, bromine, or hydrogen chloride (HBr, Br₂ or HCl), which is commonly required for the transition metal‐free aerobic oxidation of alcohols.     

Preparation and Use of Polystyryl‐DABCOF2: An Efficient Recoverable and Reusable Catalyst for β‐Azidation of α,β‐Unsaturated Ketones in Water

Novel solid fluorides were prepared to optimize the β‐azidation of α,β‐unsaturated ketones. The higher loading of these catalysts compared to that of commercially available fluorides has allowed the use of a smaller mass of catalyst helping the mixing of the reaction mixture. Porous polymeric supports have proved to be more efficient in the presence of water as reaction medium. Water has played a crucial role showing a beneficial effect on the reactivity by improving dispersion of the reaction mixture and also by avoiding organic fouling caused by the retention of the reaction mixture within the polymeric matrix. This has facilitated the recovery of the products from the catalyst. The protocol reported has allowed a significant reduction in the organic solvent required for the complete recovery of the pure product whilst leaving the catalyst clean and reusable. E‐factors are in the range of 5.9–10.5 and therefore ca. 3 times smaller than previous procedures operating under solvent‐free conditions. To further improve the efficiency of our approach we have developed a protocol operating in a continuous‐flow manner that has allowed us to achieve an E‐factor of 1.7–1.9, with a reduction of ca. 80% of the corresponding batch conditions. The continuous‐flow protocol has allowed us to minimize the use of trimethylsilyl azide making the recovery and reuse of water and catalyst 5f very efficient and simple. Finally, a novel reduction system using palladium on alumina (5 mol%) and equimolar amount of formic acid has been used in the presence of 1 equivalent of di‐tert‐butyl pyrocarbonate to set a multistep protocol operating in continuous‐flow conditions for the preparation of two representative N‐Boc‐β‐amino ketones starting from the corresponding enones with E‐factors of 3.2 and 2.7, respectively.