Simultaneous Laser Thermal Lens Spectrometric Determination of Trace Platinum and Palladium in an Aquesous Solution

A selective and sensitive method for determination of platinum and palladium(Ⅱ）in an aqueous solution simultaneously by laser thermal lens spectrometry,based on the complex reaction of 2-(3,5-dichloropyridylazo)-5-dimethylaminoamiline(3,5-diCl-PADMA) with platinum and palladium,has been developed.It is shown that the palladium complex can be fromed at room temperature, while the platinum complex can be only formed after being heated in a boiling water bath.By using this difference of reaction temperature and the characteristic of the complexes mentioned above,the method for simultaneous determination of platinum and palladium was established in an aqueous solution without a pre-separation.The results show that the dynamic linear ranges of determination for platinum and palladium are 0.005-0.04μg/mL and 0.005-0.25μg/mL respectively,and that the detection limits are both 0.002/μg/mL.The method has been applied to the determination of platinum and palladium simultaneously in alloy and catalyst samples with satisfactory results.     

Urea‐Based Porous Organic Frameworks: Effective Supports for Catalysis in Neat Water

Two urea‐based porous organic frameworks, UOF‐1 and UOF‐2, were synthesized through a urea‐forming condensation of 1,3,5‐benzenetriisocyanate with 1,4‐diaminobenzene and benzidine, respectively. UOF‐1 and UOF‐2 possess good hydrophilic properties and high scavenging ability for palladium. Their palladium polymers, Pd^II/UOF‐1 and Pd^II/UOF‐2, exhibit high catalytic activity and selectivity for Suzuki–Miyaura cross‐coupling reactions and selective reduction of nitroarenes in water. The catalytic reactions can be efficiently performed at room temperature. Palladium nanoparticles with narrow size distribution were formed after the catalytic reaction and were well dispersed in UOF‐1 and UOF‐2. XPS analysis confirmed the coordination of the urea oxygen atom with palladium. SEM and TEM images showed that the original network morphology of UOF‐1 and UOF‐2 was maintained after palladium loading and catalytic reactions.     

A mild and efficient palladium–triethylsilane system for reduction of olefins and carbon–carbon double bond isomerization

The versatility of palladium(II) acetate and palladium on activated charcoal catalysts with triethylsilane has been investigated in the hydrogenation and the isomerization of carbon–carbon double bond of 1‐alkenes. The reduction of 1‐alkenes was carried out in the presence of triethylsilane, ethanol and a catalytic amount of palladium(II) acetate or palladium on activated charcoal, at room temperature. This facile and efficient method affords high yields for hydrogenation of unsaturated alkenes to the corresponding alkanes. Then the carbon–carbon double bond isomerization of 1‐alkenes was tested using the same catalysts in the absence of solvent. The system palladium(II) acetate‐triethylsilane was found to be more effective compared with palladium on an activated charcoal–triethylsilane system at room temperature, while comparable results were obtained at 50 °C for both catalysts. Copyright © 2006 John Wiley & Sons, Ltd.     

Palladium‐Catalyzed Cascade Double C—N Bond Activation: A New Strategy for Aminomethylation of 1,3‐Dienes with Aminals

A new palladium‐catalyzed selective aminomethylation of conjugated 1,3‐dienes with aminals via double C—N bond activation is described. This simple method provides an effective and rapid approach for the synthesis of linear α,β‐unsaturated allylic amines with perfect regioselectivity. Mechanistic studies disclosed that one palladium catalyst cleaved two distinct C—N bond to furnish a cascade double C—N bond activation, in which an allylic 1,3‐diamine and allylic 1,2‐diamine were initially formed as key intermediates through the palladium‐catalyzed C—N bond activation of aminal and the α,β‐unsaturated allylic amine was subsequently produced via palladium‐catalyzed C—N bond activation of the allylic diamines.     

Silyl Ligand Mediated Reversible β‐Hydrogen Elimination and Hydrometalation at Palladium

The mechanism and origin of the facile β‐hydrogen elimination and hydrometalation of a palladium complex bearing a phenylene‐bridged PSiP pincer ligand are clarified. Experimental and theoretical studies demonstrate a new mechanism for β‐hydrogen elimination and hydrometalation mediated by a silyl ligand at palladium, which enables direct interconversion between an ethylpalladium(II) complex and an η²‐(Si‐H)palladium(0) complex without formation of a square‐planar palladium(II) hydride intermediate. The flexibility of the PSiP pincer ligand enables it to act as an efficient scaffold to deliver the hydrogen atom as a hydride ligand.     

Mizoroki–Heck and Suzuki–Miyaura reactions mediated by poly(2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid)‐stabilized magnetically separable palladium catalyst

The purpose of this work was to synthesize and characterize a new magnetic polymer nanosphere‐supported palladium(II) acetate catalyst for reactions requiring harsh conditions. In this regard, an air‐stable, moisture‐stable and highly efficient heterogenized palladium was synthesized by the coordination of palladium(II) acetate with poly(2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid)‐grafted modified magnetic nanoparticles with a core–shell structure. The structure of the newly developed catalyst was characterized using various techniques. The catalytic activity of the resultant nano‐organometallic catalyst was evaluated in Mizoroki–Heck and Suzuki–Miyaura reactions to afford the corresponding coupling products in good to excellent yields. High selectivity as well as outstanding turnover number (14 143, 4900) and turnover frequency (28 296, 7424) values were recorded for the catalyst in Suzuki–Miyaura and Mizoroki–Heck reactions, respectively. Magnetic separation and recycling of the catalyst for at least six runs became possible without any significant loss of efficiency or any detectable palladium leaching.     

Well‐Defined N‐Heterocyclic Carbene‐Palladium Complexes as Efficient Catalysts for Domino Sonogashira Coupling/Cyclization Reaction and C‐H bond Arylation of Benzothiazole

Well‐defined and air‐stable PEPPSI (Pyridine Enhanced Precatalyst Preparation Stabilization and Initiation) themed palladium bis‐N‐heterocyclic carbene complexes have been developed for the domino Sonogashira coupling/cyclization reaction of 2‐iodophenol with a variety of terminal alkynes and C‐H bond arylation of benzothiazole with aryl iodides. The PEPPSI themed palladium complexes, 2a and 2b were synthesized in good yields from the reaction of corresponding imidazolium salts with PdCl₂ and K₂CO₃ in pyridine. The new air‐stable palladium‐NHC complexes were characterized by NMR spectroscopy, X‐ray crystallography, elemental analysis, and mass spectroscopy studies. The PEPPSI themed palladium(II) bis‐N‐heterocyclic carbene complexes 2a and 2b exhibited excellent catalytic activities for domino Sonogashira coupling/cyclization reaction of 2‐iodophenol with terminal alkynes yielding benzofuran derivatives. In addition, the palladium complexes, 2a and 2b successfully catalyzed the direct C‐H bond arylation of benzothiazole with aryl iodides as coupling partners in presence of CuI as co‐catalyst.     

Prefunctionalized Porous Organic Polymers: Effective Supports of Surface Palladium Nanoparticles for the Enhancement of Catalytic Performances in Dehalogenation

Three porous organic polymers (POPs) containing H, COOMe, and COO^? groups at 2,6‐bis(1,2,3‐triazol‐4‐yl)pyridyl (BTP) units (i.e., POP‐1, POP‐2, and POP‐3, respectively) were prepared for the immobilization of metal nanoparticles (NPs). The ultrafine palladium NPs are uniformly encapsulated in the interior pores of POP‐1, whereas uniform‐ and dual‐distributed palladium NPs are located on the external surface of POP‐2 and POP‐3, respectively. The presence of carboxylate groups not only endows POP‐3 an outstanding dispersibility in H₂O/EtOH, but also enables the palladium NPs at the surface to show the highest catalytic activity, stability, and recyclability in dehalogenation reactions of chlorobenzene at 25 °C. The palladium NPs on the external surface are effectively stabilized by the functionalized POPs containing BTP units and carboxylate groups, which provides a new insight for highly efficient catalytic systems based on surface metal NPs of porous materials.     

Mechanistic Insight Leads to a Ligand Which Facilitates the Palladium‐Catalyzed Formation of 2‐(Hetero)Arylaminooxazoles and 4‐(Hetero)Arylaminothiazoles

By using mechanistic insight, a new ligand (EPhos) for the palladium‐catalyzed C−N cross‐coupling between primary amines and aryl halides has been developed. Employing an isopropoxy group at the C3‐position favors the C‐bound isomer of the ligand‐supported palladium(II) complexes and leads to significantly improved reactivity. The use of a catalyst system based on EPhos with NaOPh as a mild homogeneous base proved to be very effective in the formation of 4‐arylaminothiazoles and highly functionalized 2‐arylaminooxazoles. Previously, these were not readily accessible using palladium catalysis.     

Efficient Heterogeneous Palladium‐Catalyzed Oxidative Cascade Reactions of Enallenols to Furan and Oxaborole Derivatives

A heterogeneous palladium‐catalyzed oxidative cyclization of enallenols has been developed for the construction of highly substituted furan and oxaborole derivatives. The heterogeneous catalyst (Pd‐AmP‐MCF) exhibits high activity, high site‐ and stereoselectivity, and efficient palladium recyclability in the transformations.     

Carboxylate Switch between Hydro‐ and Carbopalladation Pathways in Regiodivergent Dimerization of Alkynes

Experimental and theoretical investigation of the regiodivergent palladium‐catalyzed dimerization of terminal alkynes is presented. Employment of N‐heterocyclic carbene‐based palladium catalyst in the presence of phosphine ligand allows for highly regio‐ and stereoselective head‐to‐head dimerization reaction. Alternatively, addition of carboxylate anion to the reaction mixture triggers selective head‐to‐tail coupling. Computational studies suggest that reaction proceeds via the hydropalladation pathway favoring head‐to‐head dimerization under neutral reaction conditions. The origin of the regioselectivity switch can be explained by the dual role of carboxylate anion. Thus, the removal of hydrogen atom by the carboxylate directs reaction from the hydropalladation to the carbopalladation pathway. Additionally, in the presence of the carboxylate anion intermediate, palladium complexes involved in the head‐to‐tail dimerization display higher stability compared to their analogues for the head‐to‐head reaction.     

Palladium‐Catalyzed Hydroaminocarbonylation of Alkenes with Amines: A Strategy to Overcome the Basicity Barrier Imparted by Aliphatic Amines

A novel and efficient palladium‐catalyzed hydroaminocarbonylation of alkenes with aminals has been developed under mild reaction conditions, and allows the synthesis of a wide range of N‐alkyl linear amides in good yields with high regioselectivity. On the basis of this method, a cooperative catalytic system operating by the synergistic combination of palladium, paraformaldehyde, and acid was established for promoting the hydroaminocarbonylation of alkenes with both aromatic and aliphatic amines, which do not react well under conventional palladium‐catalyzed hydroaminocarbonylation.     

硅胶负载钯: 一种新型有效而可循环的Heck反应的催化剂

本文报道了一种新型硅胶负载钯催化剂在Heck 反应中的应用。在硅胶负载钯催化剂,碳酸钾为碱,DMF为溶剂的反应条件下（无膦和无游离胺的存在）,碘代芳烃、溴代芳烃和活泼的氯代芳烃与烯烃发生偶联反应生成高产率相应的偶联产物。而且硅胶负载的钯催化剂经简单处理,可循环使用6次不降低活性。     

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.     

Palladium‐Catalyzed Carbonylation of 2‐Bromoanilines with 2‐Formylbenzoic Acid and 2‐Halobenzaldehydes: Efficient Synthesis of Functionalized Isoindolinones

A concise and highly versatile method for the synthesis of functionalized isoindolinones is reported. Various 2‐bromoanilines undergo palladium‐catalyzed carbonylation with 2‐formylbenzoic acid under a convenient and mild procedure to give good to excellent yields of the corresponding isoindolinones. Additionally, 2‐halobenzaldehydes can be applied as substrates in palladium‐catalyzed double‐carbonylation to provide identical compounds in moderate to good yields.     

Palladium‐Catalyzed Fluorination of Cyclic Vinyl Triflates: Effect of TESCF3 as an Additive

A method for the palladium‐catalyzed fluorination of cyclic vinyl triflates has been developed. As with several previous palladium‐catalyzed fluorination reactions using fluoride salts, controlling the regioselectivity presented a challenge in developing a practical synthetic procedure. The addition of triethyl(trifluoromethyl)silane (TESCF₃) was found to effectively address this problem and resulted in drastically improved regioselectivities in this palladium‐catalyzed fluorination reaction. This discovery, along with the use of a new biarylphosphine ligand, allowed for the development of an efficient and highly regioselective protocol for the fluorination of vinyl triflates. This method is compatible with a range of sensitive functional groups and provides access to five‐, six‐, and seven‐membered cyclic vinyl fluorides.     

Palladium magnetic nanoparticle‐polyethersulfone composite membrane as an efficient and versatile catalytic membrane reactor

Developing polymer catalytic membrane reactors is an aim due to its outstanding advantages. In this paper, a novel catalytic membrane containing palladium‐supported magnetic nanoparticles is introduced. Silica‐iron oxide core shell nanoparticles were first prepared and functionalized by phosphine ionic liquid functionalized poly(ethylene glycol). The modified magnetic nanoparticles were used as support for immobilization of palladium. The final palladium‐immobilized nanoparticles were used as active filler for the preparation of membrane reactor. The prepared membranes were characterized, and their activities were tested in carbon‐carbon bond formation and catalytic reduction. The catalytic membrane showed good performance in the mentioned reactions.     

Palladium‐Catalyzed Oxygenative Cross‐Coupling of Ynamides and Benzyl Bromides by Carbene Migratory Insertion

A palladium‐catalyzed oxygenative cross‐coupling of ynamides and benzyl bromides has been developed. After subsequent hydrogenation, α,α‐disubstituted amide derivatives were obtained in good yields. Migratory insertion of α‐oxo palladium carbene species, generated by intermolecular oxidation, is proposed as the key step in this reaction. The study demonstrates the potential of ynamides to serve as carbene precursors in palladium‐catalyzed C?C bond‐forming cross‐coupling reactions.     

A Palladium‐Nanoparticle and Silicon‐Nanowire‐Array Hybrid: A Platform for Catalytic Heterogeneous Reactions

We report the development of a silicon nanowire array‐stabilized palladium nanoparticle catalyst, SiNA‐Pd. Its use in the palladium‐catalyzed Mizoroki‐Heck reaction, the hydrogenation of an alkene, the hydrogenolysis of nitrobenzene, the hydrosilylation of an α,β‐unsaturated ketone, and the C‐H bond functionalization reactions of thiophenes and indoles achieved a quantitative production with high reusability. The catalytic activity reached several hundred‐mol ppb of palladium, reaching a TON of 2 000 000.     

Template‐less synthesis of polymer hollow spheres: an efficient catalyst for Suzuki coupling reaction

We report here a method for the preparation of polymer hollow spheres in which 3‐aminoquinoline (3‐AQ) and palladium acetate were used as precursors. During the reaction 3‐AQ was oxidized and formed poly(3‐AQ). IR and Raman spectra provided information on the chemical structure of the polymer. The oxidation state of palladium was confirmed by X‐ray photoelectron spectroscopic analysis. Transmission and scanning electron microscopy were used to determine the size and morphology of the polymer. The palladium–poly(3‐AQ) supramolecular system was used as an effective catalyst for the Suzuki coupling reaction of aryl halides in the absence of a phosphine ligand. Copyright © 2013 John Wiley & Sons, Ltd.