Palladium-catalyzed Research Articles

Asymmetric 2,4-Dienylation/[4 + 2] Annulation Cascade to Construct Fused Frameworks via Auto-Tandem Palladium Catalysis.

A palladium catalyzed tandem reaction between ortho-functionalized aryl enones and 2,4-dienyl carbonates has been presented, proceeding through sequential 2,4-dienylation/Michael addition/π-σ-π isomerization/allylic alkylation. A broad array of enantioenriched architectures having fused and spirocyclic frameworks are constructed in moderate to excellent yields and stereoselectivity. Notably, the intrinsic intramolecular Diels-Alder reaction pattern of the dienylated intermediates is well reversed via Pd(0)-π-Lewis base catalysis.

Escape from Palladium: Nickel-Catalyzed Catellani Annulation.

While Catellani reactions have become increasingly important for arene functionalizations, they have been solely catalyzed by palladium. Here we report the first nickel-catalyzed Catellani-type annulation of aryl triflates and chlorides to form various benzocyclobutene-fused norbornanes in high efficiency. Mechanistic studies reveal a surprising outer-sphere concerted metalation/deprotonation pathway during the formation of the nickelacycle, as well as the essential roles of the base and the triflate anion. The reaction shows a broad functional group tolerance and enhanced regioselectivity compared to the corresponding palladium catalysis.

Photoinduced Nitrogen-to-Alkyl Radical Relay Heck Reaction of o-Alkylbenzamides with Vinyl Arenes by Palladium Catalysis.

Here, a palladium-catalyzed photoinduced N-to-alkyl radical relay Heck reaction of o-alkylbenzamides at benzylic sites with vinyl arenes is described. The reaction employs neither exogeneous photosensitizers nor external oxidants. It is proposed to proceed via a N-to-alkyl hybrid palladium-radical mechanism which occurs under mild conditions that are compatible with a wide range of functional groups. The products are easily transformed to azepinone derivatives, which are prevalent in pharmaceuticals and natural products.

‘Homeopathic’ palladium catalysis? The observation of distinct kinetic regimes in a ligandless Heck reaction at (ultra-)low catalyst loadings

The catalytic behaviour of ‘ligandless’ palladium(II) acetate in the Heck arylation reaction of iodobenzene with methyl acrylate is examined at (ultra-)low catalyst loadings using in situ spectroscopy. The study reveals two distinctive kinetic regimes with distinct Pd orders. A simplified microkinetic model revealed the presence of at least two kinetically competent catalysts, represented by a monomeric (Pd1) and dimeric (Pd2) species. The relative catalytic activity and deactivation rates for both species can also be estimated from the experimental results. This work provides direct kinetic evidence that a higher-order Pd species can be more active than a monomeric species, and the key role played by catalyst deactivation, particularly at higher catalyst loadings. This implies that lowering the catalyst loading may be an effective strategy to combat catalyst deactivation without necessarily incurring significant deterioration in reaction rate.

Deoxygenative Hydrogenation of Aromatic Aldehydes and Ketones by Pd Nanoparticles on Carbon Nitride

Key words palladium catalysis - nanoparticles - deoxygenative hydrogenation - photocatalysis - carbon nitride

Performance Investigation of Dual Trench Split-Control-Gate MOSFET as Hydrogen Gas Sensor: A Catalytic Metal Gate Approach

In this article, Dual Trench Split-Control-Gate MOSFET (DT-SCG-MOSFET) based hydrogen gas sensor considering catalytic palladium metal gate approach is simulated using SILVACO ATLAS TCAD. The inner gate architecture in addition to the outer control gates provides enhanced carrier control. Shift in surface potential, subthreshold current, linear current and threshold voltage are used to investigate the performance of the proposed gas sensor. The contribution of analog metrices like the transconductance and parasitic capacitances are explored thoroughly. Sensitivity as a function of subthreshold current as well as change in threshold voltage for the presence and absence of hydrogen gas molecules have been discussed. Results exhibit the superiority of the proposed gas sensor compared with the reported models in terms of sensitivity and Ion/Ioff ratio and suitable for hydrogen gas detection.

Convective Flow-Assisted Catalytic Propulsion of Polymer Beads Coated with Pd Nanoparticles for the Detection of Enzyme Inhibitors and Industrial Effluents

Ultrasensitive detection of enzyme inhibitors and heavy metal contaminants in effluents constitutes a major interdisciplinary research area. Multiple methods based on colorimetry, conductance measurement, reactivity estimation, etc., have been developed in this direction, which often involve the use of sophisticated equipment and complex methodologies. Herein, we present a simple, table-top technique for the detection of enzyme inhibitors and industrial effluents using convective flow-assisted propulsion of catalytic palladium nanoparticle (NP)-coated polymer motors in solution. The motors display buoyancy-driven self-propulsion, which is further enhanced in the presence of secondary catalysts like catalase and horseradish peroxidase, generating auxiliary convection in the experimental chamber. The convection and the motor propulsion were sensitive toward molecules that inhibited the enzyme activity, thereby offering a platform for using NP-coated catalytic motors as dynamic sensing probes for harmful chemicals in liquids. Initially, effective sensing of trace amounts of Cu2+, Ag+, and Cd2+ ions was performed based on the reduced propulsion of the catalytic motors through the fuel solution. The detection limit of Cu2+ in the aqueous environment was found to be less than the permissible limit suggested by the Central Ground Water Board (CGWB), Government of India. Experiments were also conducted to demonstrate the generic applicability of motor-based detection of different enzyme inhibitors (in the micromolar concentration range), such as a flavonoid (hydroquinone) and an aromatic dipeptide (diphenylamine). Finally, it was demonstrated that the catalytic NP-coated polymer motors could also be used effectively to detect industrial effluents using samples containing different compounds that acted as enzyme inhibitors. A simple model connecting the enzyme inhibition and motor propulsion speed is presented to explain the experimental observations.

Free amino group-directed C(sp2)–H arylation of α-amino-β-aryl esters by palladium catalysis

Native amino-directed palladium-catalyzed C(sp3)–H activation/functionalization has been developed for modification of α-amino acids and peptides. Herein a palladium(II)-catalyzed C(sp2)–H arylation of α-amino-β-aryl esters has been disclosed, using the native amino as the directing group. A variety of chiral α-amino-β-aryl esters can be functionalized to give the corresponding ortho-substituted mono- and di-arylated products.

Distance controlled graphyne-like binuclear palladium catalyst for accelerating nitrobenzene reduction

The diatomic catalyst synthesized by high-temperature thermal cracking usually undergoes structural reorganization of raw materials, increasing the difficulty in studying the structure-activity relationship of the catalysts. Herein, starting from the synthesis methodology, we adjust the atomic spacing of dual-Pd-site catalysts to 0.4 and 0.8 nm by regulating the monomer structure of graphyne. The model experiment of nitrobenzene reduction shows that graphyne catalyst (TEGY-Pd) with closer palladium atom spacing (0.4 nm) show a faster reaction rate (1.57 min−1), good universality and cyclic stability in catalytic process than that of graphdiyne catalyst (TEGDY-Pd) which has longer palladium atom spacing. Moreover, the theoretical calculation shows that the excellent catalytic performance of TEGY-Pd is original from the synergetic catalysis of the closer diatomic palladium to the nitro group in adsorption and electron transport process. This work provided a new idea to precisely control the metal atomic spacing and revealed the structure activity relationship of binuclear catalysts.

Synthesis of Fused Lactones through Transition‐Metal‐Catalyzed peri C−H Functionalization

AbstractThe rhodium(III)‐catalyzed dehydrogenative cyclization of 9‐anthracenecarboxylic acids and 2‐substituted 1‐naphthoic acids proceeds through peri C−H bond cleavages to produce fused lactones. These aromatic carboxylic acids also undergo dehydrogenative coupling with styrenes and successive Wacker‐type cyclization under palladium catalysis to construct 3‐benzylidenebenzo[de]isochromen‐1‐one frameworks.

Photoinduced Palladium-Catalyzed 1,2-Difunctionalization of Electron-Rich Olefins via a Reductive Radical-Polar Crossover Reaction

Palladium-catalyzed cross-coupling reactions belong to the most important transformations for the construction of C–C or C-heteroatom bonds. More recently, the photochemical activation of palladium complexes emerged as a key strategy to leverage palladium catalysis at room temperature beyond the scope of conventional cross-coupling chemistry. Herein, we report on the photoinduced palladium-catalyzed 1,2-difunctionalization reaction of electron-rich olefins. Mechanistic experiments and computational studies reveal that this reaction proceeds via the addition of an alkyl radical, followed by the oxidation of a radical intermediate to access carbocation intermediates, which are inaccessible via classic thermal reaction conditions. The carbocation can then be applied to a variety of secondary C–C or C–N bond-forming reactions. This strategy now allows a general approach toward densely functionalized unsymmetric 1,1-bis(heterocyclyl)alkanes.

Chiral Aldehyde-Palladium Catalysis Enables Asymmetric Synthesis of α-Alkyl Tryptophans via Cascade Heck-Alkylation Reaction.

The first catalytic asymmetric cascade Heck-alkylation reaction of NH2-unprotected amino acid esters with N-(2-iodophenyl)allenamides is reported in this work. Under the promotion of a combining catalytic system comprising a chiral aldehyde, a chiral palladium complex, and the Lewis acid ZnCl2, the title reaction takes place smoothly, giving optically active α-alkyl tryptophan derivatives in moderate to good yields and excellent enantioselectivities. The target products can be converted into other structurally complex chiral indoles without the loss of enantioselectivities.

Pd and Cu Synergistic Catalysis for the Synthesis of α,α-Disubstituted Amino Acids

Key words copper catalysis - palladium catalysis - α,α-disubstituted amino acids - synergistic catalysis - aldimines

Mono-ortho-Alkylation of Meta-Substituted Iodoarenes Using a Cycloolefin Ligand in a Catellani-Type Reaction

Key words palladium catalysis - Catellani-type reaction - mono-ortho-alkylation - mono-ortho-methylation

Palladium-Catalyzed [4+2] Annulation to Access [6.7]-Fused N-Heterocycles

Key words palladium catalysis - [4+2] annulation - fused N-heterocycles

An efficient construction of quinoline-based hybrid scaffolds through palladium-catalyzed C[sbnd]S coupling

Organosulfides have prodigious value and significance in synthetic and biological chemistry. In this context, an efficient and operationally simple constructionof quinoline based hybrid scaffolds has been achieved through palladium-catalyzed CS coupling synthetic strategy. This strategy employs the reaction of 2-(2-chloroquinolin-3-yl)-3-phenylthiazolidin-4-ones with thiophenols under palladium catalysis. Some notable features of this methodology like high efficiency, good functional group toleranceand easily obtainable substrates provides apromising platform. The employed strategyis anticipated to be further utilized in developing direct transformations of inert haloquinoline into synthesis of medicinally important building blocks.

Synergistic Palladium/Chiral Phosphoric Acid-Catalyzed Kinetic Resolution via Stereoselective Intramolecular Substitution of Unactivated Allylic Alcohols.

This paper reports the kinetic resolution of racemic secondary alcohols (O-nucleophiles) via stereoselective intramolecular allylic substitution. The reaction was enabled by synergistic palladium and chiral phosphoric acid catalysis and produced chiral cis-1,3-disubstituted 1,3-dihydroisobenzofurans with a selective factor of up to 60.9 and a diastereomeric ratio of up to 7.8:1. Asymmetric synthesis of a compound with antihistaminic activity was demonstrated as the application of this methodology.

Dual-Ligand Catalyst for the Nondirected C-H Olefination of Heteroarenes.

Pd(II)-catalyzed nondirected C-H functionalization of heteroarenes is a significant challenge for the following reasons: poor reactivity of electron-deficient heterocycles and the unproductive coordination of Lewis basic nitrogen atoms. Existing methodologies using palladium catalysis often employ a large excess of heterocycle substrates to overcome these hurdles. Despite recent advances in nondirected functionalization of arenes that allow them to be used as limiting reagents, the reaction conditions are incompatible with electron-deficient heteroarenes. Herein we report a dual-ligand catalyst that enables Pd(II)-catalyzed nondirected C-H olefination of heteroarenes without using a large excess of substrate. In general, the use of 1-2 equiv of substrates was sufficient to obtain synthetically useful yields. The reactivity was rationalized by the synergy between two types of ligands: a bidentate pyridine-pyridone ligand promotes C-H cleavage; the monodentate heterocycle substrate acts as a second ligand to form a cationic Pd(II) complex that has high affinity for arenes. The proposed dual-ligand cooperation is supported by a combination of X-ray, kinetics, and control experiments.

Pd/Ni Co‐catalyzed Selective Cross‐Coupling of Aryl Bromides and Aryl Fluorosulfonates at Room Temperature

AbstractMultimetallic catalysis can effectively enhance the selectivity for the heterocoupling product over homocoupling products in cross‐electrophilic couplings. We report the selective cross‐coupling of aryl bromides with aryl fluorosulfonates via palladium and nickel cooperative catalysis for the synthesis of biaryls, which can be carried out at room temperature while having marvelous chemoselectivity. In addition, the reaction also has a good performance on the gram‐scale reaction.

Stereoselective Synthesis of Tetraarylethylenes Enabled by Reductive anti-1,2-Dimetallation of Alkynes.

Tetraarylethylenes (TAEs) have been gaining attention from various scientific disciplines for their characteristic chemical and physical properties. From the synthetic perspective, however, efficient methods for the selective synthesis of different isomers of TAEs are still underdeveloped. Here, we report the regio- and stereoselective synthesis of TAEs by means of sodium-promoted reductive anti-1,2-dimagnesiation of alkynes. Subsequent transmetallation to zinc generates trans-1,2-dizincioalkenes, which underwent the stereoselective arylation under a palladium catalysis to afford a variety of TAEs that had been difficult to prepare according to the conventional procedures. In addition, the present method accommodates not only diarylacetylenes but also alkyl aryl acetylenes and thus enables to synthesize a wide range of all-carbon tetrasubstituted alkenes.