A series of (NHC)Pd(N˄O)(OAc) complexes: synthesis,characterization and catalytic activities towards desulfinative Sonogashira coupling of arylsulfonyl hydrazides with arylalkynes

A series of well-defined N-heterocyclic carbene palladium (II) complexes with general formula (NHC)Pd(N^˄O)(OAc) were prepared through reaction of Pd (NHC)(OAc)₂(H₂O) with 1-methyl-1H-pyrazole-3-carboxylic acid or 1-methyl-1H-indazole-3-carboxylic acid in the presence of K₂CO₃. These complexes were then used for desulfinative Sonogashira coupling of arylsulfonyl hydrazides with terminal alkynes. With low catalyst loading, all synthesized palladium compounds exhibited moderate to high catalytic activities for the reactions.     

Double-coupling of dibromo arenes with aryltriolborates for synthesis of diaryl-substituted planar frameworks

A new method for simple and practical synthesis of diaryl-substituted arenes using potassium aryltriolborates was developed. Double-cross-coupling of dibromo arenes with aryltriolborates was carried out in the presence of a palladium catalyst, such as Pd(OAc)₂, Pd(PPh₃)₄ or Pd(OAc)₂/BIPHEP. The use of CuCl (40 mol %) with a palladium catalyst was found to be highly effective to give diaryl-substituted aromatic compounds in good yields.     

Reaction of coordinated phosphines: VI. Divalent palladium promoted cleavage of carbon—phosphorus bonds in tertiary phosphines

The important role of divalent palladium in the cleavage of carbon—phosphorus bond of tertiary phosphines is revealed by the study of the phenylation in the Pd(OAc)₂Ph₃P-styrene system under various conditions; reaction atmosphere, ratio of Ph₃P/Pd(OAc)₂, and addition of ethanol or Cu^II(OAc)₂ · H₂O.     

醋酸钯催化甲苯中无配体的 Suzuki 反应

 报道了一种甲苯中醋酸钯催化无配体的 Suzuki 反应体系. 以 K₃PO₄·7H₂O 为碱, 在该体系中可高效进行芳基溴代物和芳基硼酸的 Suzuki 反应, 且具有反应条件温和、无需惰性气体保护等特点. 在 n(ArBr) = 0.5 mmol, n(ArB(OH)₂) = 0.75 mmol, x(Pd(OAc)₂) = 1 mol%, n(K₃PO₄·7H₂O) = 1.0 mmol, v(甲苯) = 2 ml 的优化条件下, 4-溴硝基苯和苯硼酸在 75 °C 反应 5 min, 分离收率即达 99%, TOF 高达 1 188 h?1.     

Autocatalytic Intermolecular versus Intramolecular Deprotonation in C?H Bond Activation of Functionalized Arenes by Ruthenium(II) or Palladium(II) Complexes

The activation of the C? H bond of 1‐phenylpyrazole ( 2 ) and 2‐phenyl‐2‐oxazoline ( 3 ) by [Ru(OAc)₂(p‐cymene)] is an autocatalytic process catalyzed by the co‐product HOAc. The reactions are indeed faster in the presence of acetic acid and water but slower in the presence of a base K₂CO₃. A reactivity order is established in the absence of additives: 2‐phenylpyridine>2‐phenyl‐2‐oxazoline>1‐phenylpyrazole (at RT). The accelerating effect of added acetate ions reveals an intermolecular deprotonation after C? H bond activation by a cationic Ru^II center (S_E3 mechanism). The reactions of 1‐phenylpyrazole and 2‐phenyl‐2‐oxazoline first lead to the neutral cyclometalated complexes A₂ and A₃ ligated by one acetate. The latter dissociate to the cationic complexes B₂ ⁺ and B₃ ⁺ , respectively, and acetate. A slow incorporation of one or two D atoms into 2 , 3 , and 2‐phenylpyridine ( 1 ) was observed in the presence of deuterated acetic acid. The “reversibility” of the C? H bond activation/deprotonation takes place from the cationic complexes B _n ⁺ (n=1–3). They are also involved in oxidative additions to PhI, which are rate‐determining and lead to the mono‐ and bis‐phenylated products at high temperatures. A general mechanism is proposed for the arylation of arenes 1–3 catalyzed by [Ru(OAc)₂(p‐cymene)]. In contrast, the reaction of Pd(OAc)₂ with 2‐phenylpyridine ( 1 ), is much faster: Pd(OAc)₂>[Ru(OAc)₂(p‐cymene)]. Since the kinetics is not affected by added acetates, the reaction proceeds through a CMD mechanism assisted by a ligated acetate (intramolecular process) and is irreversible. A bis‐cyclometalated Pd^II^Pd^II dimer D′₁ is formed whose bielectronic electrochemical oxidation leads to a [Pd^III^Pd^III]²⁺ dimer, in agreement with the result of a reported chemical oxidation used in arene functionalizations catalyzed by Pd(OAc)₂.     

Synthesis of (−)‐Erythrodiene and (+)‐7‐Epispirojatamol via Intramolecular Pd‐Catalyzed Allylzincation

Two spirobicyclic sesquiterpenoids, (−)‐erythrodiene ( 1 ) and (+)‐7‐epispirojatamol ( 30 ), were synthesized in enantiomerically pure form via an intramolecular allylzincation process. The allylzinc species were formed in the presence of Et₂Zn via transmetallation of a catalytically generated allylpalladium intermediate. Several Pd catalysts were tested for this transformation, and [Pd(OAc)₂]/Bu₃P (1 equiv.) was found to be, by far, the most effective. Whereas the preparation of 1 involved allylzincation of a tethered terminal olefin, 30 was formed via a novel intramolecular allyl zincation of a methyl ketone. Both reactions showed the same stereochemical preference, yielding the spirobicyclic products in 95 : 5 and 4 : 1 diastereoisomer ratios, respectively.     

Pd(OAc)2-catalyzed orthogonal synthesis of 2-hydroxybenzoates and substituted cyclohexanones from acyclic unsaturated 1,3-carbonyl compounds

A Pd-catalyzed orthogonal synthesis of substituted 2-hydroxybenzoates and substituted cyclohexanones was developed for the first time. The substituted 2-hydroxybenzoates were obtained from acyclic unsaturated 1,3-carbonyl compounds using a combination of catalytic Pd(OAc)₂ and Cu(OAc)₂. On the other hand, the substituted cyclohexanones were produced from similar substrates via catalytic Pd(OAc)₂ and hydrogen chloride. Each transformation was clean, easy to work up, provided the desired compounds in good purities, and did not require column chromatography purification.     

Reactions of diazoalkanes with unsaturated compounds. 14. Reactions of diazomethane,diazocyclopropane, and methyl diazoacetate with 1,1,2,2-tetrafluoro-3-vinylcyclobutane and 2,3,3-trifluoro-1-vinylcyclobutene to form [3+2] and [1+2] cycloadducts

The reactions of diazomethane and diazocyclopropane generated in situ with 1,1,2,2-tetrafluoro-3-vinylcyclobutane (1) and 2,3,3-trifluoro-1-vinylcyclobutene (2) proceeded at the double bond of the substituent as the 1,3-dipolar cycloaddition to form the corresponding 1-pyrazolines. Under the conditions of thermolysis (340—400 °C), the resulting cyclobutylpyrazolines 4 and 5 selectively lost the dinitrogen molecule to generate 3-cyclopropyl-1,1,2,2-tetrafluorocyclobutane (6) or 1,1,2,2-tetrafluoro-3-spiropentylcyclobutane (7), respectively, in high yields. In the presence of Pd(acac)₂, the reactions of these fluorine-containing unsaturated compounds and 2-chloro-1,1,2-trifluoro-3-vinylcyclobutane (3) with diazomethane gave rise directly to cyclopropane derivatives 6, 11, and 12, respectively. The reactions of compounds 1 and 2 with methyl diazoacetate in the presence of Rh₂(OAc)₄ proceeded analogously to yield cis- and trans-disubstituted cyclopropanes.     

Palladium-Catalyzed Coupling Reaction of Iodouracil Having Acetamidine Moiety with Olefins

The reaction of 6-[1-Aza-2-(dimethylamino)prop-l-enyl]-5-iodo-1,3-dimethyluracil (3) with various olefins in the presence of a catalytic amount of Pd(OAc)₂ and 1.5 equiv. of K₂CO₃ in DMF at 120 °C gave the pyrido[2,3-d]pyrimidine derivatives (5a-b and 7a-d) in moderate to high yield.     

Reactivity of 6-(2-tolyl)- and 6-(2,6-xylyl)-2,2′-bipyridines with palladium(II) derivatives. Selective C(sp)H vs. C(sp)H activation

Two new 6-substituted 2,2′-bipyridines, L, 6-(2-tolyl)bipy, L¹, and 6-(2,6-xylyl)bipy, L², have been synthesized. Their reactions with Na₂[PdCl₄] or {Pd(OAc)₂} afford either 1:1 adducts [Pd(L)X₂] (X=Cl, OAc) or five-membered cyclometallated derivatives [Pd(L¹-H)X] arising from C(sp²)H activation. From the chloro-alkyl intermediates [Pd(L)(Me)Cl], in the presence of Na[BAr′₄] (Ar′=3,5-(CF₃)₂C₆H₃), cationic species [Pd(L)(Me)(S)]⁺ (L=L¹, L²; S=CH₃CN) can be obtained. At variance, in less coordinating solvents, e.g. dichloromethane, unexpected activation of a C(sp³)H bond occurs with loss of methane, to afford 6-membered cyclometallated derivatives. The latter species were isolated as [Pd(L-H)(PPh₃)][BAr′₄].     

Preparation and Characterization of Some Novel Diphenylphosphine Hydrazones and Semicarbazones and Their Metal Complex Derivatives

Interaction of hydrazones and semicarbazones derivatives I _{a ? t} with diphenylchlorophosphine II , gave new compounds III _a?t , and their complexation ability towards various divalent metal acetates Mn(OAc)₂. 4H₂O, Co(OAc)₂. 4H₂O, Ni(OAc)₂. 4H₂O, and Cu(OAc)₂. H₂O, in organic solvents are described. The metal/ phosphorsemi-carbazones ratios are measured and the results discussed. All these complexes are insoluble in organic solvents and in water. The structures of the isolated products were proposed on the basis of microanalyical data, TGA, IR, (UV/ VIS), (MS), and ¹H, ¹³C, and ³¹P-NMR spectroscopic analyses and magnetic susceptibility. The proposed structure of the complexes is based on a 1: 2 metal: ligand ratio. All of the complexes are found to have an octahedral geometry, with the exception of the square planar copper (II) complexes. The corrosion inhibition of aluminium and copper in 1 M HCl and chromium–nickel steel in crude oil using III_n have been studied by weight loss method.     

Metal-proton interactions in palladium(II) and rhodium(I) complexes ofortho-alkylanilines

Summary Reaction of 1 equivalent ofo-alkylaniline with Pd(OAc)₂ gave the acetate bridged complexes [Pd(OAc)₂L]₂. The^*H n.m.r. spectra showed downfield shifts for theo-benzylic protons indicating an above-plane geometry involving a significant interaction with the metal orbitals. Similar interactions were found for Pd(OAc)₂L₂ and Pd(OAc)₂L(L) (L= differento-alkylaniline; t-butylpyridineetc.) prepared from the dimer and for Rh(CO)₂Cl(L) complexes. Theo-benzylic carbons of the palladium complexes did not show downfield shifts in the¹³C n.m.r. spectra.     

Facile Hydrolysis and Alcoholysis of Palladium Acetate

Palladium(II) acetate is readily converted into [Pd₃(μ²‐OH)(OAc)₅] ( 1 ) in the presence of water in a range of organic solvents and is also slowly converted in the solid state. Complex 1 can also be formed in nominally anhydrous solvents. Similarly, the analogous alkoxide complexes [Pd₃(μ²‐OR)(OAc)₅] ( 3 ) are easily formed in solutions of palladium(II) acetate containing a range of alcohols. An examination of a representative Wacker‐type oxidation shows that the Pd‐OH complex 1 and a related Pd‐oxo complex 4 can be excluded as potential catalytic intermediates in the absence of exogenous water.     

Synthesis and characterization of orthopalladated complexes of 4-chloro benzoylmethylene triphenylphosphorane and their application in Suzuki cross-coupling

Orthopalladated binuclear complexes (1) have been prepared by refluxing a mixture of the phosphorus ylide (ClBPPY) with Pd(OAc)₂ in CH₂Cl₂. Complex 1 reacts with ligands (L) to give (L = PPh₃ (2), Me₃Py (3)). Cyclopalladated complexes are highly efficient catalysts for the Suzuki reactions of aryl bromide with aryl boronic acid. The monomeric complexes 2 and 3 are more active than the dimer 1. Palladium mirror was observed, indicating the involvement of classic Pd(0)/Pd(II) catalytic cycle using these cyclopalladated complexes. The coupling of aryl bromide with aryl boronic acid gave the desired biphenyl congeners in good to excellent yields. We tested the various bases, finding that inorganic bases work better than organic ones.     

High Nuclearity Bimetallic Rhodium–Palladium Carbonyl Cluster Complexes. Synthesis and Characterization of Rh6(CO)16[Pd(PBu t 3)]3 and Rh6(CO)16[Pd(PBu t 3)]4

The reaction of Rh₄(CO)₁₂ with Pd(PBu ^t ₃)₂ yielded the high nuclearity bimetallic hexarhodium-tripalladium cluster complex Rh₆(CO)₁₆[Pd(PBu ^t ₃)]₃, 10, in 11% yield. Compound 10 was converted to the hexarhodium-tetrapalladium cluster Rh₆(CO)₁₆[Pd(PBu ^t ₃)]₄, 11, in 62% yield by reaction with an additional quantity of Pd(PBu ^t ₃)₂. Both compounds were characterized crystallographically. Structurally, both compounds consist of an octahedral cluster of six rhodium atoms with sixteen carbonyl ligands analogous to that of the known compound Rh₆(CO)₁₆. Compound 10 also contains three Pd(PBu ^t ₃) groups that bridge three Rh–Rh bonds along edges of the Rh₆ octahedron to give an overall D₃ symmetry to the Rh₆Pd₃ cluster. Compound 11 contains four edge bridging Pd(PBu ^t ₃) groups distributed across the Rh₆ octahedron to give an overall D_2d symmetry to the Rh₆Pd₄ cluster. Each Rh–Pd connection in both compounds contains a bridging carbonyl ligand that helps to stabilize the bond between the Pd(PBu ^t ₃) groups and the Rh atoms. Both compounds can be regarded as Pd(PBu ^t ₃) adducts of Rh₆(CO)₁₆.     

Regioselective synthesis of 2,3-disubstituted 1-alkyl pyrrolo[2,3-b] quinoxalines through palladium-catalyzed Heck reaction of chalcones and evaluation of their anti-bacterial activities

The regioselective synthesis of 1-alkyl-2-aryl-3-acyl pyrrolo[2,3-b]quinoxalines through palladium-catalyzed Heck coupling reaction/heteroannulation was reported. The reaction of N-alkyl/benzyl-3-chloroquinoxaline-2-amines with chalcones catalyzed by Pd(OAc)₂ in the presence of KO^tBu, as the base, in DMSO afforded the desired products in good-to-high yields. The MIC and MBC determinations revealed that these compounds could be used in the future research works for the development of antibiotics.     

Catalytic C-phenylation of methyl acrylate with tetraphenylantimony(v) halides and carboxylates

Catalytic C-phenylation of methyl acrylate to methyl cinnamate with the Ph₄SbX complexes (X = F, Cl, Br, OH, OAc, O₂CEt) in the presence of the palladium compounds PdCl₂, Pd(OAc)₂, Pd₂(dba)₃, Pd(Ph₃P)₂Cl₂, and Pd(dppf)Cl₂ (dba is dibenzylideneacetone and dppf is bis(diphenylphosphinoferrocene)) was studied in organic solvents (MeCN, THF, DMF, MeOH, and AcOH). The highest yield of methyl cinnamate (73% based on the starting organometallic compound) was obtained for the Ph₄SbCl—PdCl₂ (1 : 0.04) system in acetonitrile.     

Mechanism of the formation of palladium complexes serving as catalysts in hydrogenation reactions : I. Reactions of complexes with molecular hydrogen

The interaction of Ph₃PPD(OAc)₂₂ with molecular H₂ yields a binuclear complex of zero-valent palladium, (Ph₃P)₂Pd₂. This complex interacts reversibly with H₂ in CH₂Cl₂, yielding (Ph₃P)₂Pd₂H₂. In argon atmosphere (Ph₃P)₂Pd₂ reacts with [Ph₃PPd(OAc)₂₂ to form a binuclear complex of Pd^I with a metal—metal bond. These data, as well as the results of kinetic studies of the reactions between [Ph₃PPd(OAc)₂₂ and H₂, are in agreement with an autocatalytic mechanism for the process, including catalysis of the reduction of Pd^II complexes by the Pd⁰ compounds. It has been established that the synthesized compound of Pd^II, Pd^I and Pd⁰ with the ratio P/Pd?1, are inactive in the hydrogenation of unsaturated compounds. The catalytically active complex (PPh)₂Pd₅ is formed when palladium acetate reacts with (Ph₃P)₂Pd₂ in the presence of H₂. The same compound is formed when a solution of (Ph₃P)₂Pd₂ is treated with a mixture of H₂ and O₂ (or H₂O₂ in an atmosphere of H₂). (PPh)₂Pd₅ is an effective catalyst for the hydrogenation of olefins, dienes, acetylenes, aldehydes, organic peroxides, quinones, O₂, Schiff bases, and nitro, nitroso, and azo compounds.     

A Novel Synthesis of Berbines1-Synthesis of 2,3-Dimethoxy-10,11-Methylenedioxyberbine by Use of Palladium Catalyzed Insertion of Carbon Monoxide

Palladium catalyzed amidation has recently been reported for the synthesis of benzolactams². We wish to report a simple and efficient method for the synthesis of berbines by the Palladium catalyzed insertion of carbon monoxide under mild reaction conditions such as an atmospheric pressure of carbon monoxide at 95° by use of a catalytic amount of Pd(OAc)₂ and PPh₃ in presence of a tertiary amine. The approach has wider applicability in the berbine synthesis³ as examplified by the synthesis of 2,3-dimethoxy-10,11-methylene-dioxyberbine 7. The bromo-1-benzyl tetrahydroisoquinoline derivative 5 ⁴, the key precursor, was prepared from the known reaction sequence involving an Schotten-Baumann condensation⁵ and B.N. reaction followed by sodium borohydride reduction.     

Preparations of Saturated N‐P‐N Type Secondary Phosphine Oxides and their Applications in Cross‐Coupling Reactions

A series of cyclohexane‐1,2‐diamine ( 3a – 3d ) and benzene‐1,2‐diamine derivatives ( 3e – 3h ) were pre‐ pared. Followed by hydrolysis, the reaction of 3a – 3c with PCl₃ successfully led to the formation of cor‐ responding metastable saturated heteroatom‐substituted secondary phosphine oxides (HASPO 4a – 4c ), a tautomer of the saturated heteroatom‐substituted phosphinous acid (HAPA). Whereas ambient‐stable diamine‐coordinated palladium complexes were obtained, HAPA‐coordinated palladium complexes were not successfully synthesized. The molecular structures of HASPO 4c , Pd(OAc)₂(3a) , PdBr₂(3b) and Pd(OAc)₂(3c) and [Cu(NO₃)(3d)⁺][NO₃ ^? ] were determined by single‐crystal X‐ray diffraction method. Catalysis of in‐situ Suzuki‐Miyaura cross‐coupling reactions for aryl bromides and phenylboronic acid using diamine 3a as ancillary ligand showed that the optimized reaction condition at 60 °C is the combination of 2 mmol % 3a /3.0 mmol KOH/1.0 mL 1,4‐dioxane/1 mmol % Pd(OAc)₂. Moreover, moderate reactivity was observed when using aryl chlorides as substrates (supporting infor‐ mation). When diamine 3d was employed in Heck reaction, good tolerance of functional groups of aryl bromides were observed while using 4‐bromoanisole and styrene as substrates. The optimized condi‐ tion for Heck reaction at 100 °C is 3 mmol % 3d /3.0 mmol CsF/1.0 mL toluene/3 mmol % Pd(OAc)₂. In general, cyclohexane‐1,2‐diamine derivatives exhibited better catalytic properties than those of benzene‐1,2‐diamines.