Palladium‐Catalyzed Synthesis of (Hetero)Aryl Alkyl Sulfones from (Hetero)Aryl Boronic Acids,Unactivated Alkyl Halides,and Potassium Metabisulfite

A palladium‐catalyzed one‐step synthesis of (hetero)aryl alkyl sulfones from (hetero)arylboronic acids, potassium metabisulfite, and unactivated or activated alkylhalides is described. This transformation is of broad scope, occurs under mild conditions, and employs readily available reactants. A stoichiometric experiment has led to the isolation of a catalytically active dimeric palladium sulfinate complex, which was characterized by X‐ray diffraction analysis.     

Palladium‐Catalyzed Synthesis of (Hetero)Aryl Alkyl Sulfones from (Hetero)Aryl Boronic Acids,Unactivated Alkyl Halides,and Potassium Metabisulfite

A palladium‐catalyzed one‐step synthesis of (hetero)aryl alkyl sulfones from (hetero)arylboronic acids, potassium metabisulfite, and unactivated or activated alkylhalides is described. This transformation is of broad scope, occurs under mild conditions, and employs readily available reactants. A stoichiometric experiment has led to the isolation of a catalytically active dimeric palladium sulfinate complex, which was characterized by X‐ray diffraction analysis.     

Mild and rational synthesis of palladium complexes comprising C(4)-bound N-heterocyclic carbenes

Oxidative addition of pyridyl-functionalised 4-iodoimidazolium salts to palladium(0) gives catalytically active complexes in which the N-heterocyclic carbene is bound to the palladium(II) centre in a non-classical bonding mode via C(4).     

Investigation of the Catalytic Activity of a 2‐Phenylidenepyridine Palladium(II) Complex Bearing 4,5‐Dicyano‐1,3‐bis(mesityl)imidazol‐2‐ylidene in the Mizoroki‐Heck Reaction

The phenylidenepyridine (ppy) palladacycles [PdCl(ppy)(IMes)] ( 4 ) [IMes = 1,3‐bis(mesityl)imidazol‐2‐ylidene] and [PdCl(ppy){(CN)₂IMes}] ( 6 ) [(CN)₂IMes = 4,5‐dicyano‐1,3‐bis(mesityl)imidazol‐2‐ylidene] were prepared by facile two step syntheses, starting with the reaction of palladium(II) chloride with 2‐phenylpyridine followed by subsequent addition of the NHC ligand to the precatalyst precursor [PdCl(ppy)]₂. Suitable crystals for the X‐ray analysis of the complexes 4 and 6 were obtained. It was shown that 6 has a shorter NHC‐palladium bond than the IMes complex 4 . The difference of the palladium carbene bond lengths based on the higher π‐acceptor strength of (CN)₂IMes in comparison to IMes. Thus, (CN)₂IMes should stabilize the catalytically active central palladium atom better than IMes. As a measure for the π‐acceptor strength of (CN)₂IMes compared to IMes, the selone (CN)₂IMes · Se ( 7 ) was prepared and characterized by ⁷⁷Se‐NMR spectroscopy. The π‐acceptor strength of 7 was illuminated by the shift of its ⁷⁷Se‐NMR signal. The ⁷⁷Se‐NMR signal of 7 was shifted to much higher frequencies than the ⁷⁷Se‐NMR signal of IMes · Se. Catalytic experiments using the Mizoroki‐Heck reaction of aryl chlorides with n‐butyl acrylate showed that 6 is the superior performer in comparison to 4 . Using complex 6 , an extensive substrate screening of 26 different aryl bromides with n‐butyl acrylate was performed. Complex 6 is a suitable precatalyst for para‐substituted aryl bromides. The catalytically active species was identified by mercury poisoning experiments to be palladium nanoparticles.     

Anti-Markovnikov hydroaminations of styrene catalyzed by palladium(II) N-heterocyclic carbene complexes under conventional and microwave heating

Six palladium(II) complexes with benzimidazole-based N-heterocyclic carbene ligands were synthesized by transmetallation reactions between silver(I) N-heterocyclic carbene complexes and PdCl₂(PhCN)₂. The complexes were characterized by physicochemical and spectroscopic methods. The palladium complexes were tested as catalysts for intermolecular hydroamination reactions of styrene with various anilines in ionic liquids under both conventional and microwave heating. All of these complexes proved to be catalytically active in these reactions. The anti-Markovnikov addition products were selectively obtained by using 1 mol% of the palladium complex.     

Guanidine‐Functionalized Resin‐Supported Pd(0) Catalyst: Activity,Reusability, and Redeposition of Active Pd Species in Heck Vinylation

The guanidine‐functionalized resin‐supported Pd(0) catalyst [GDR·Pd(0)] is highly active in Heck reaction of aryl bromides with acrylic acid or styrene without the need to exclude air. The catalyst can be recycled at least 9 times without significant loss of activity in N‐methyl‐2‐pyrrolidone at 140 °C. The Heck reaction proceeds homogeneously with dissolved palladium species and the dissolved active palladium species can redeposit onto the surface of catalyst in the reaction. The XRD peak shifting of Pd phases in the catalyst provides the evidence for the re‐deposition of the active palladium species.     

Hydrolysis of amide bond in histidine-containing peptides promoted by chelated amino acid palladium(II) complexes: dependence of hydrolytic pathway on the coordination modes of the peptides

Hydrolytic reactions between cis-[Pd( -Ala-N,O)Cl₂]⁻ and cis-[Pd( -Ala-N,O)(H₂O)₂]⁺, in which -Ala is alanine coordinated through N and O atoms, and N-acetylated peptides -histidylglycine (MeCO-His-Gly), glycyl- -histidine (MeCO-Gly-His), glycylglycyl- -histidine (MeCO-Gly-Gly-His) and glycyl- -histidylglycine (MeCO-Gly-His-Gly) were studied by ¹H NMR spectroscopy. All reactions were carried out in the pH range 2.0–2.5 and two different temperatures, 22 and 60°C. In the reactions of these two palladium(II) complexes with MeCO-His-Gly, complete hydrolysis of the amide bond involving carboxylic group of histidine occurs in less than 24 h. The cleavage is regioselective. With peptides containing free a carboxylic group of histidine, MeCO-Gly-His and MeCO-Gly-Gly-His, palladium(II) complex promote the cleavage of the MeCO–Gly and Gly–Gly amide bonds. No cleavage of the Gly–His amide bond was observed. The mechanism of these hydrolytic reactions involves release of -Ala ligand and aquation of the palladium(II) complex chelated to the substrate through the imidazole N-3 atom and deprotonated nitrogen atom of the amide bond involving amino group of histidine. This aqua complex represents a catalytically active form different from the initially added catalytically inactive complex. In the reactions of palladium(II) complexes with tripeptide MeCO-Gly-His-Gly, two amide bonds, MeCO–Gly and His–Gly, were cleaved. The mechanism of the cleavage of these amide bonds is correlated with two different palladium(II)–substrate catalytically active forms. These findings contribute to the better understanding of selective cleavage of peptides and proteins and must be taken into consideration in designing new reagents for this purpose.     

Sonogashira coupling of aryl halides catalyzed by palladium on charcoal

With the proper choice of solvent, palladium on charcoal acts as an efficient catalyst in the Sonogashira cross-coupling reaction of aryl bromides. The catalytically active species in the process is probably palladium, which leaches into the solution but returns onto the surface of the charcoal at the end of the reaction.     

Palladium-catalyzed allylic oxidation of olefins by t-butyl hydroperoxide and tellurium(IV) oxide

Treatment of several cyclic olefins, β-pinene, allylbenzene, and estragole with palladium(II) salt in acetic acid in the presence of t-butyl hydroperoxide and tellurium(IV) oxide afforded mainly the corresponding allylic acetates. The reaction proceeded catalytically with palladium(II) salt, t-BuOOH working as a reoxidizing agent.     

The irreversible formation of palladium carbide during hydrogenation of 1-pentyne over silica-supported palladium nanoparticles: in situ Pd K and L3 edge XAS

The catalytically active phase of silica-supported palladium catalysts in the selective and non-selective hydrogenation of 1-pentyne was determined using in situ X-ray absorption spectroscopy at the Pd K and L(3) edges. Upon exposure to alkyne, a palladium carbide-like phase rapidly forms, which prevents hydrogen to diffuse into the bulk of the nano-sized particles. Both selective and non-selective hydrogenation occur over carbided particles. The palladium carbide-like phase is stable under reaction conditions and only partially decomposes under high hydrogen partial pressure. Non-selective hydrogenation to pentane is not indicative of hydride formation. The palladium carbide phase was detected in the EXAFS analysis and the K edge XANES showed representative features.     

High-throughput kinetic study of hydrogenation over palladium nanoparticles: combination of reaction and analysis

The hydrogenation of 1-acetylcyclohexene, cyclohex-2-enone, nitrobenzene, and trans-methylpent-3-enoate catalyzed by highly active palladium nanoparticles was studied by high-throughput on-column reaction gas chromatography. In these experiments, catalysis and separation of educts and products is integrated by the use of a catalytically active gas chromatographic stationary phase, which allows reaction rate measurements to be efficiently performed by employing reactant libraries. Palladium nanoparticles embedded in a stabilizing polysiloxane matrix serve as catalyst and selective chromatographic stationary phase for these multiphase reactions (gas-liquid-solid) and are coated in fused-silica capillaries (inner diameter 250 microm) as a thin film of thickness 250 nm. The palladium nanoparticles were prepared by reduction of palladium acetate with hydridomethylsiloxane-dimethylsiloxane copolymer and self-catalyzed hydrosilylation with methylvinylsiloxane-dimethylsiloxane copolymer to obtain a stabilizing matrix. Diphenylsiloxane-dimethylsiloxane copolymer (GE SE 52) was added to improve film stability over a wide range of compositions. Herein, we show by systematic TEM investigations that the size and morphology (crystalline or amorphous) of the nanoparticles strongly depends on the ratio of the stabilizing polysiloxanes, the conditions to immobilize the stationary phase on the surface of the fused-silica capillary, and the loading of the palladium precursor. Furthermore, hydrogenations were performed with these catalytically active stationary phases between 60 and 100 degrees C at various contact times to determine the temperature-dependent reaction rate constants and to obtain activation parameters and diffusion coefficients.     

A Turn‐On Fluorescent Probe for Highly Selective and Sensitive Detection of Palladium

A novel turn‐on fluorescent probe for the detection of palladium has been designed. The probe can selectively and sensitively detect palladium in solution, and the limit of detection was calculated to be 11.4 nmol·L^?1. Furthermore, the probe was successfully used for fluorescence imaging of palladium in living cells.     

TMEDA in Iron‐Catalyzed Hydromagnesiation: Formation of Iron(II)‐Alkyl Species for Controlled Reduction to Alkene‐Stabilized Iron(0)

N,N,N′,N′‐Tetramethylethylenediamine (TMEDA) has been one of the most prevalent and successful additives used in iron catalysis, finding application in reactions as diverse as cross‐coupling, C?H activation, and borylation. However, the role that TMEDA plays in these reactions remains largely undefined. Herein, studying the iron‐catalyzed hydromagnesiation of styrene derivatives using TMEDA has provided molecular‐level insight into the role of TMEDA in achieving effective catalysis. The key is the initial formation of TMEDA–iron(II)–alkyl species which undergo a controlled reduction to selectively form catalytically active styrene‐stabilized iron(0)–alkyl complexes. While TMEDA is not bound to the catalytically active species, these active iron(0) complexes cannot be accessed in the absence of TMEDA. This mode of action, allowing for controlled reduction and access to iron(0) species, represents a new paradigm for the role of this important reaction additive in iron catalysis.     

Exclusive Detection of Sub‐Nanomolar Levels of Palladium(II) in Water: An Excellent Probe for Multiple Applications

A new colorimetric probe has been developed for the detection and estimation of Pd^II at sub‐nanomolar concentrations. The probe consisted of rhodamine (signaling unit), which was linked with a bis‐picolyl moiety (binding site) through a phenyl ring. Pd^II induced opening of the spirolactam ring of the probe with the generation of a prominent pink color. The excellent selectivity of the probe towards Pd^II over Pd⁰ or Rh^II ensured its potential utility for the detection of residual palladium contamination in pharmaceutical drugs and in Pd‐catalyzed reactions. The probe showed a “turn‐on” (bright yellow) fluorescence upon the addition of Pd^II, which made it suitable for the detection of Pd contaminants in mammalian cells.     

Palladium acetate-catalyzed cyclization reaction of 2,3-allenoic acids in the presence of simple allenes: an efficient synthesis of 4-(1'-bromoalk-2'(Z)-en-2'-yl)furan-2(5H)-one derivatives and the synthetic application

We have realized a cyclization reaction of 2,3-allenoic acids 1 in the presence of simple alkyl- or aryl-substituted allenes 3. In this reaction, the cyclic oxypalladation of 2,3-allenoic acid with Pd(II) would afford the furanonyl palladium intermediate 2, which could be trapped by the simple allene to afford a pi-allylic intermediate anti-9. This intermediate anti-9 could be nucleophilically attacked by Br- to yield 4-(1'-bromoalk-2'(Z)-en-2'-yl)furan-2(5H)-one derivatives Z-5 and Pd(0). The in-situ formed Pd(0) was efficiently converted to the catalytically active Pd(II) species by benzoquinone in HOAc. The functional groups, such as malonate, acetoxyl, and phthalic amide in allene 3, are tolerable under the current conditions. High efficiency of chirality transfer was observed when optically active 2,3-allenoic acids were used, which reveals that the formation of the intermediates 2 was a highly stereoselective anti-oxypalladation process. The highly selective formation of Z-isomer may be explained by face-selective coordination of allene 3 with the palladium atom in intermediate 2: the palladium atom coordinates to the terminal C=C double bond of allene 3 from the face opposite to the substituent group to avoid the steric congestion. The products Z-5 could be further elaborated via the S(N)2 nucleophilic substitution with amine or sodium benzenesulfinate, the reduction of the C-Br bond by NaBH(4), and the CuBr.SMe(2)-catalyzed S(N)2'-substitution with CH(3)MgBr.     

La（III）催化磷酸二（4－硝基苯酚）酯水解研究

The catalytic hydrolysis of bis（4-nitrophenyl）phosphate （BNPP） by lanthanum（Ⅲ） ion in the presence of amino-alcoholic ligands： diethanolamine （DEA） and triethanolamine （TEA）, was investigated kinetically at 30 ℃. The results indicated that the dinuclear dihydroxo complexes formed by lanthanum（Ⅲ） ion with aminoalcoholic ligands might be the catalytically active species which catalyze the hydrolysis of BNPP to different extents and the catalytic mechanism was believed to involve the synergism of double Lewis acid activation of the substrate and an intramolecular nucleophilic attack of a bridging oxo ligand.     

Tridentate N-donor palladium(II) complexes as efficient coordinating quadruplex DNA binders

Fifteen complexes of palladium, platinum, and copper, featuring five different N‐donor tridentate (terpyridine‐like) ligands, were prepared with the aim of testing their G‐quadruplex–DNA binding properties. The fluorescence resonance energy transfer melting assay indicated a striking positive effect of palladium on G‐quadruplex DNA stabilization compared with platinum and copper, as well as an influence of the structure of the organic ligand. Putative binding modes (noncoordinative π stacking and base coordination) of palladium and platinum complexes were investigated by ESI‐MS and UV/Vis spectroscopy experiments, which all revealed a greater ability of palladium complexes to coordinate DNA bases. In contrast, platinum compounds tend to predominantly bind to quadruplex DNA in their aqua form by noncoordinative interactions. Remarkably, complexes of [Pd(ttpy)] and [Pd(tMebip)] (ttpy=tolylterpyridine, tMebip=2,2′‐(4‐p‐tolylpyridine‐2,6‐diyl)bis(1‐methyl‐1H‐benzo[d]imidazole)) coordinate efficiently G‐quadruplex structures at room temperature in less than 1 h, and are more efficient than their platinum counterparts for inhibiting the growth of cancer cells. Altogether, these results demonstrate that both the affinity for G‐quadruplex DNA and the binding mode of metal complexes can be modulated by modifying either the metal or the organic ligand.     

Direct synthesis of Fe(III) immobilized Zr‐based metal–organic framework for aerobic oxidation reaction

A Zr‐based metal–organic framework with bipyridine units (UiO‐67) has been utilized for the immobilization of catalytically active iron species via a post‐synthetic metalation method. UiO‐67 bipyridine MOF was synthesized through a simple solvothermal method and was shown to have a UiO‐type structure. Post‐synthetic metalation of UiO‐67 MOF was performed for the immobilization of the catalytically active FeCl₃. FT‐IR and EDX element map suggested that FeCl₃ is coordinately bonded to the UiO‐67 bipyridine framework. The synthesized UiO‐67‐FeCl₃ catalyst was used for the aerobic oxidation of alcohols and benzylic compounds in the presence of molecular oxygen. In addition, the UiO‐67‐FeCl₃ catalyst can be reused as a solid heterogeneous catalyst without compromising its activity and selectivity.     

Size-controlled synthesis and characterization of polyvinyl alcohol coated palladium nanoparticles

In order to synthesize stable, catalytically active palladium nanoparticles with low polydispersity, a one-pot synthesis by the facile reduction of palladium chloride with citric acid in an aqueous solution of steric stabilizer polyvinyl alcohol (PVA) has been developed. The resulting nanoparticles are highly water-dispersible, excellent electro-catalysts, and have long shelf life. The palladium nanoparticles have been characterized by physico-chemical, spectroscopic, microscopic, and CV studies. The average size of the nanoparticles can be readily tuned from 8.1 to 53 nm by controlling the extent of reflux for mixtures containing suitable concentrations of metal ion, reducing agent and capping polymer, which also influence the size. Despite the surface-protecting action of PVA, the palladium nanoparticles are electro-catalytically active and exhibit size-dependent electro-catalytic behavior.     

Visible‐Light‐Induced CO Release from a Therapeutically Viable Tryptophan‐Derived Manganese(I) Carbonyl (TryptoCORM) Exhibiting Potent Inhibition against E. coli

The first visible‐light‐activated carbon‐monoxide‐releasing molecule (CO‐RM) to exhibit a potent effect against Escherichia coli is described. The easily prepared tryptophan‐derived manganese‐containing complex (TryptoCORM) released 1.4 moles of CO at 465 nm, and 2 moles at 400 nm. A comprehensive synthetic, mechanistic and microbiological study into the behaviour of TryptoCORM is reported. The complex is thermally stable (i.e., does not release CO in solution in the absence of light), shows low toxicity against mammalian cells and releases tryptophan on photoinduced degradation, all of which point to TryptoCORM being therapeutically viable.