Palladium acetate—Sodium chloride

Diphenylimidazole with palladium acetate forms the cyclometallated complex 80 (X = OAc) (97AOC491). The acetate group is replaced by chloride or bromide when 80 (X = OAc) reacts with sodium chloride or lithium bromide, respectively, to give 80 (X = C1, Br). Bromide with diethyl sulfide forms the mononuclear complex 81. Similar reactions are known for 1 -acetyl-2-phenylimidazole (96JOM(522)97). 1,5-Bis(A -methylimidazol-2-yl)pen-tane with palladium(II) acetate gives the cyclometallated complex 82 (OOJOM (607)194). 

Carboxylic acids can be prepared in moderate-to-high yields by treatment of diazonium fluoroborates with carbon monoxide and palladium acetate or copper(II) chloride. The mixed anhydride ArCOOCOMe is an intermediate that can be isolated. Other mixed anhydrides can be prepared by the use of other salts instead of sodium acetate." An arylpalladium compound is probably an intermediate." ... 

Another easily available palladium compound is PdCl2 however, it has low or no activity. The chloride ion in the coordination sphere of palladium seems to inhibit the coordination of two moles of butadiene to form the bis-77-allylic complex. However, PdCl2 can be used in the presence of an excess of bases, such as KOH, NaOH, sodium phenoxide, sodium acetate, potassium acetate, sodium methoxide, or tertiary amines. These bases deprive the chloride ion from the coordination sphere of palladium to form the active species. Thus, very stable and easily prepared... 

Davies (69) has carried out a series of isomerization experiments in a medium consisting of acetic acid, palladium(II) chloride, and sodium chloride, the latter in a 1 1 mole ratio. In this system sodium 1,2,3,4-/ii,/x -dichloropalladium(II) was assumed to be present ... 

A flask was charged with 4-bromo-iodobenzene (0.079 mol), 4-methoxy-2-methyl-phenyl boronic acid (0.087 mol), palladium acetate (0.004 mol), and triphenyl phosphine (0.008 mol) and then treated with 200 ml acetone and 250 ml 2M NaHCO i. The mixture was refluxed at 65°C for 18 hours and was then treated with water and diethyl ether and the organic layer isolated. This layer was washed with 40 ml saturated sodium chloride solution and water, dried over MgSC>4, filtered, and concentrated. The residue was purified by column chromatography using silica gel with CH2C12/ hexane, 1 1, and then recrystallized in / , 7 3, respectively, and 16.4 g of product isolated. 

Methods (i) and (ii) require palladium(II) salts as reactants. Either palladium acetate, palladium chloride or lithium tetrachloropalladate(II) usually are used. These salts may also be used as catalysts in method (iii) but need to be reduced in situ to become active. The reduction usually occurs spontaneously in reactions carried out at 100 °C but may be slow or inefficient at lower temperatures. In these cases, zero valent complexes such as bis(dibenzylideneacetone)palladium(0) or tetrakis(triphenylphos-phine)palladium(O) may be used, or a reducing agent such as sodium borohydride, formic acid or hydrazine may be added to reaction mixtures containing palladium(II) salts to initiate the reactions. Triarylphosphines are usually added to the palladium catalysts in method (iii), but not in methods (i) or (ii). Normally, 2 equiv. of triphenylphosphine, or better, tri-o-tolylphosphine, are added per mol of the palladium compound. Larger amounts may be necessary in reactions where palladium metal tends to precipitate prematurely from the reaction mixtures. Large concentrations of phosphines are to be avoided, however, since they usually inhibit the reactions. 

Aryl chlorides Aryl chlorides will substitute alkenes only under very special conditions, and then catalyst turnover numbers are generally not very high. Palladium on charcoal in the presence of triethylphos-phine catalyzes the reaction of chlorobenzene with styrene,58 but the catalyst becomes inactive after one use.59 Examples employing an activated aryl chloride and highly reactive alkenes, such as acrylonitrile, with a palladium acetate-triphenylphosphine catalyst in DMF solution at ISO C with sodium acetate as base react to the extent of only 51% or less.60 Similar results have been reported for the combination of chlorobenzene with styrene in DMF-water at 130 C, using sodium acetate as the base and palladium acetate-diphos as a catalyst.61 Most recently, a method for reacting chlorobenzene with activated alkenes has been claimed where, in addition to the usual palladium dibenzilideneacetone-tri-o-tolylphosphine catalyst, nickel bromide and sodium iodide are added. It is proposed that an equilibrium concentration of iodobenzene is formed from the chlorobenzene-sodium iodide-nickel bromide catalyst and the iodoben-zene then reacts in the palladium-catalyzed alkene substitution. Moderate to good yields were reported from reactions carried out in DMF solution at 140 C 62... 

The residue was subjected to azeotropic operation with toluene two times, and ether was added to the residue. The precipitate derived from trioxane was removed by filtration and washed with ether, and the combined ethereal solutions were concentrated under reduced pressure. The residue was dissolved in ethyl acetate, and the solution was washed with water and aqueous saturated solution of sodium chloride, was dried, and was concentrated to give 4 g of an oily material. The oily material was dissolved in 20 ml of methanol and to the solution was added 20 ml of aqueous 1 N solution of sodium hydroxide, and the mixture was stirred for 14 hours at room temperature. After removal of methanol under reduced pressure, water was added to the mixture, and this solution was acidified to pH 3 with aqueous 2 N hydrochloric acid. The mixture was extracted five times with ethyl acetate, and the ethyl acetate extract was dried and concentrated to give 3.5 g of crude crystals. After addition of ethanol to the crude crystals, the crude crystals were filtered. The filtrate was concentrated, and to the residue was added ethanol and ethyl acetate, and precipitate was collected by filtration. The combined amount of the crude crystals was 1.6 g. After the combined crude crystals were methylated with diazomethane, the reaction product was dissolved in 20 ml of ethyl acetate. To this solution was added 1.5 g of sodium acetate and 300 mg of 10% palladium-carbon, and the mixture was stirred for 2 hours under hydrogen. Then, the reaction product was filtered, and after addition of aqueous saturated solution of sodium hydrogen carbonate to the filtrate, the mixture was extracted two times with ethyl acetate. The extract was washed with an aqueous saturated solution of sodium chloride, dried, and concentrated to give 1.3 g of crude crystals. The crude crystals were recrystallized from ethyl acetate to yield 765 mg of the title compound (melting point 134-135°C, yield 43%). 

Over 35 years ago, Richard F. Heck found that olefins can insert into the metal-carbon bond of arylpalladium species generated from organomercury compounds [1], The carbopalladation of olefins, stoichiometric at first, was made catalytic by Tsutomu Mizoroki, who coupled aryl iodides with ethylene under high pressure, in the presence of palladium chloride and sodium carbonate to neutralize the hydroiodic acid formed (Scheme 1) [2], Shortly thereafter, Heck disclosed a more general and practical procedure for this transformation, using palladium acetate as the catalyst and tri-w-butyl amine as the base [3], After investigations on stoichiometric reactions by Fitton et al. [4], it was also Heck who introduced palladium phosphine complexes as catalysts, enabling the decisive extension of the ole-fination reaction to inexpensive aryl bromides [5],... 

To a mixture of the iodonium salt (172 mg, 0.46 mmol) and palladium acetate (4 mg, 5 mol%) was added sodium bicarbonate (77 mg, 0.92 mmol) followed by the cyclic carbonate (110 mg, 0.46 mmol) in DMF (5 ml), under nitrogen, at room temperature. After stirring for 2 h, the reaction mixture was quenched with saturated aqueous ammonium chloride solution and extracted with ether (2 x 20 ml). The extract was dried, the solvent removed and the residue chromatographed on silica (ethyl acetate-hexanes 1 4) to afford 4-phenylvinyl-5-benzyloxymethyl-1,3-dioxol-2-one (140 mg, 97%), m.p. not given. 

To a stirred mixture of the iodonium salt (197 mg, 0.5 mmol), palladium acetate (5.6 mg) and sodium bicarbonate (420 mg, 5 mmol) in DMF (2 ml) was added butenone (17.5 mg, 2.5 mmol), under argon, at room temperature. After 2 h, precipitation of palladium black was observed then, saturated aqueous ammonium chloride was added to the reaction mixture, followed by extraction with ethyl acetate. The organic layer was dried, the solvent evaporated and the residue purified by flash chromatography (hexanes-ethyl acetate) to give trans, trans-6-phenyl-hexa-3,5-diene-2-one (63 mg, 73%), m.p. not given. 

For cases in which vinylation with higher olefins has been studied, conflicting results have been reported. In one case, it has been reported (29) that olefins give predominantly 2-substitution—e,g.y l-penten-2-yl acetate (I) from pentene when a palladium acetate-acetic acid system is used. On the other hand, a buffered (sodium acetate) acetic acid solution of palladium chloride has been reported (58) to give 1-substitu-tion—e.g., 2-hexen-l-yl acetate (II) from hexene. Propylene has been... 

Dehalooenation Chromous chloride. Copper powder-Benzoic acid. Dimethyl sulfoxide-NaH. Hydrazine-Palladium. Iron pentacarbonyl. Lithium-l-Butanol-THF. Magnesium-Iodine-Ether. Methyllithium. Sodium acetate. Sodium iodide. Zinc dust. Zinc dust-Ethanol (see Allene, preparation. Hexafluoro-2-butyne, preparation). 

Palladium(II) chloride (1.0 g., 5.6 mmoles), 0.66 g. (11.3 mmoles) of sodium chloride, and 0.93 g. (11.3 mmoles) of sodium acetate are dissolved in 100 ml. of glacial acetic acid at 85°. The solution is filtered through a fluted filter paper, and 1.1 ml. (10 mmoles) of 2-methyl-2-pentene is added to the stirred filtrate. The mixture is kept at 85° until the color has completely changed from red to yellow (approx. 30 minutes). The solution is then poured into 500 ml. of H20, and the solution is extracted four times with 50-ml. portions of dichloromethane. The combined extracts are consecutively washed with water, aqueous sodium hydrogen carbonate, and water. They... 

On balance, palladium offers the best combination of activity and selectivity at reasonable cost, and for these reasons has become the basis of the most successful commercial alkyne hydrogenation catalysts to date. Because of their inherently high activity, these catalysts contain typically less than 0.5 % (by weight) of active metal-to preserve selectivity at high alkyne conversion. Despite the prominence of these catalysts, other active metals are used in fine chemicals applications. Of particular utility is the nickel boride formulation formed by the action of sodium borohydride on nickel(II) acetate (or chloride). Reaction in 95 % aqueous ethanol solution yields the P2-Ni(B) catalyst and selectivity in alkyne semi-hydrogenation has been demonstrated in the reaction of 3-hexyne to form cw-3-hexene in 98 % yield [15,16] ... 

A series of Pd-catalyzed intramolecular Heck reactions of N-(2-halophenyl)-substituted enaminones was performed by Pombo-Villar et al. [114]. The reactions were performed in the presence of palladium acetate with a phosphonium ligand as catalyst, sodium acetate, and tetrabutylammonium chloride (TBACl) as the PTC catalyst in DMF solution to afford desired coupling product in 25 to 99% yields (Eq. 79). 

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