Palladium chloride-free catalysts

Phenylpropanolamine. - With catalyst prepared as previously described from 0.5g of palladium chloride and 3g of charcoal, it was possible to reduce two portions of 9.8g of isonitrosopropio-phenone (0.06 mol), dissolved in 150 cc. of absolute alcohol containing 7. Og of hydrogen chloride, to phenylpropanolamine in from 145 - 190 minutes with yields of the isolated chloride from 9.4g to 11. Og, or 84 to 98% of the theoretical. After recrystallization from absolute alcohol the salt melted at 191°. The free base was obtained by treating an aqueous solution of the hydrochloride with alkali on cooling, the liberated amino alcohol solidified and after recrystallization from water melted at 103°."... 

Palladium catalysts that are free of halide ions effect the dimerization and carboxylation of butadiene to yield 3,8-nonadienoate esters. Palladium acetate, solubilized by a tertiary amine or an aromatic amine, gives the best yields and selectivities (equation 57).87 Palladium chloride catalyzes the hydrocarboxylation to yield primarily 3-pentenoates.88 The hydrocarboxylation of isoprene and chloroprene is regio-selective, placing the carboxy function at the least-hindered carbon (82% and 71% selectively) minor amounts of other products are obtained (equation 58). Cyclic dienes such as 1,3-cyclohexadiene and 1,3-cyclooctadiene are similarly hydrocarboxylated. 

A sample of activated carbon having high adsorptive capacity is warmed with dilute aqueous nitric acid. The resulting mixture is filtered, washed with water until free of acid, and dried at 200°. Twelve grams of the treated carbon, 8 g. of palladium chloride, and 24 ml. of commercial formalin are mixed thoroughly and treated with 48 ml. of 50% aqueous potassium hydroxide solution. The reaction mixture is held below room temperature during this operation. The solid obtained is removed by filtration, washed with water until free of alkali, and then dried at 120°. The resulting catalyst contains about 30% palladium. 

However, efforts were also directed to the development of phosphine-free catalysts. For example, the ligand-free Pd(OAc)2 promoted Suzuki reaction in water was reported using microwave heating. In this way, a low palladium loading (0.4 mol.%) was required and the cross coupling proceeded quickly (5-10 min reaction time), using boronic acids and aryl iodides, bromides and chlorides. 

A rapid MW-assisted palladium-catalyzed coupling of heteroaryl and aryl boronic acids with iodo and bromo-substituted benzoic acids, anchored on TentaGel has been achieved [222]. An environmentally friendly Suzuki cross-coupling reaction has been developed that uses polyethylene glycol (PEG) as the reaction medium and palladium chloride as a catalyst [223]. A solvent-free Suzuki coupling has also been reported on palladium-doped alumina in the presence of potassium fluoride as base [224]. This approach has been extended to the Sonogashira coupling reaction wherein terminal alkynes couple readily with aryl or alkenyl iodides on palladium-doped alumina in the presence of triphenylphosphine and cuprous iodide (Scheme 8.89) [225]. 

Atom C-1 in 315 is in the oxidation stage of an aldehyde, or a ketone in 1-alkylated products. The necessary solvolytic attack of the enolic double bond requires substoichiometric amounts of a catalyst such as mercuric acetate or palladium chloride and one equivalent of acid (e.g.,methanesulfonic acid) for binding the liberated diisopropylamine. If the 4-hydroxy group is free, then when using methanol as solvent, anomeric lactol ethers 316 are formed with high yields [Eq. (92)]. 

The reactivity of furan derivatives in palladium-catalyzed desulfitative arylation was studied. Alkyl-substituted furan derivatives were successfully coupled with a variety of benzenesulfonyl chlorides using a phosphine-free catalyst regioselective arylation at C-5 of the furan was observed in all cases (14S2515). 

Method A. Cool a solution of the nitrate-free dichloride, prepared from or equivalent to 5 0 g. of palladium or platinum, in 50 ml. of water and 5 ml. of concentrated hydrochloric acid in a freezing mixture, and treat it with 50 ml. of formahn (40 per cent, formaldehyde) and 11 g. of the carrier (charcoal or asbestos). Stir the mixture mechanically and add a solution of 50 g. of potassium hydroxide in 50 ml. of water, keeping the temperature below 5°. When the addition is complete, raise the temperature to 60° for 15 minutes. Wash the catalyst thoroughly by decantation with water and finally with dilute acetic acid, collect on a suction filter, and wash with hot water until free from chloride or alkali. Dry at 100° and store in a desiccator. 

In another nonelectrolytic process, arylacetic acids are converted to vi c-diaryl compounds 2A1CR2COOH —> ArCR2CR2Ar by treatment with sodium persulfate (Na2S20g) and a catalytic amount of AgNOs." Both of these reactions involve dimerization of free radicals. In still another process, electron-deficient aromatic acyl chlorides are dimerized to biaryls (2 ArCOCl —> ArAr) by treatment with a disilane RsSiSiRs and a palladium catalyst." " ... 

The groups R2N and Cl can be added directly to alkenes, allenes, conjugated dienes, and alkynes, by treatment with dialkyl-V-chloroamines and acids. " These are free-radical additions, with initial attack by the R2NH- radical ion. " N-Halo amides (RCONHX) add RCONH and X to double bonds under the influence of UV light or chromous chloride. " Amines add to allenes in the presence of a palladium catalyst. ... 

For nickel(O) complexes prepared from Ni(r -cod)2 and an excess of the free NHC, it was shown that they exhibit outstanding catalytic activity in the Kumada-Corriu reaction at room temperature toward unreactive substrates like aryl chlorides and even aryl fluorides.Again, an essential element of these catalysts is the need for sterically demanding NHC ligands as observed for the palladium catalysts. 

Although the Sonogashira reaction is normally performed with a copper cocatalyst, a copper-free, one-pot procedure for direct coupling with l-aryl-2-trimethylsilylacetylenes has been developed <2005T2697>. The procedure uses a mixture of palladium acetate and tri(o-tolyl)phosphine as catalyst in the presence of tetra- -butylammonium chloride... 

In new studies heteropoly acids as cocatalysts were found to be very effective in combination with oxygen in the oxidation of ethylene.1311 Addition of phosphomo-lybdic acid to a chloride ion-free Pd(II)-Cu(II) catalyst system results in a great increase in catalytic activity and selectivity.1312 Aerobic oxidation of terminal alkenes to methy ketones can be performed with Pd(OAc)21313 or soluble palladium complexes. Modified cyclodextrins accelerates reaction rates and enhance selectivities in two-phase systems under mild conditions.1315 1316... 

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