Palladium catalyst, preparation

The catalyst is previously prepared in an apparatus for catalytic hydrogenation, in which are placed 0.5 g. of palladous chloride, 3.0 g. of Norite, and 20 ml. of distilled water. The bottle is swept out with hydrogen and then shaken with hydrogen for 2-3 hours at 2-3 atmospheres (40 lb.) pressure. The palladium on carbon is collected on a Biichner funnel, washed with five 50-ml. portions of distilled water, then with five 50-ml. portions of 95% ethanol, and finally twice with ether. Upon drying, about 3 g. of the catalyst is obtained. It is stored in a vacuum desiccator over solid sodium hydroxide. If the reduction of the chloro-lepidine does not proceed normally, the used catalyst should be removed by suction filtration and a fresh 3-g. portion of catalyst added. Failure of the reduction step is usually due to an inactive catalyst or to impurities in the acetic acid or chlorolepidine. The palladium catalysts, prepared as described elsewhere in this volume, are presumably also satisfactory for the reduction of 2-chlorolepidine (p. 77). 

Enantioselective allylations of a-nitro ketones and a-nitro esters with allyl acetates are carried out in the presence of 2 equiv of alkali metal fluorides (KF, RbF, CsF) and 1 mol% palladium catalysts prepared in situ from Pd2(dba)3-CHC13 and chiral phosphine ligands. Moderate enantio-selectivity (ca 50% ee) is reported for allylation of cx-nitroketones (Eq. 5.60). The highest selectivity (80% ee) is observed for allylation of the reaction of tert-butyl ester (Eq. 5.61).93... 

A solution of 31.8 g (0.74 mole) of 3-(2-benzylmethylaminoacetyl) methanesulfonanilide methanesulfonate in 700 ml of absolute ethanol is reduced in an atmospheric hydrogenation unit (2 to 5 p.s.i. g positive pressure) during 24 hours with a 10% palladium catalyst prepared from 320 mg of palladium chloride and 2.0 g of pulverized charcoal. After absorption of the calculated amount of hydrogen, the catalyst is filtered, the filtrate concentrated to about 100 ml, mixed with about 500 ml of ether, resulting in precipitation of a white solid weighing 24.3 g (96%), M.P. 201-203.5°C. Two recrystallizations from ethanol (35 ml/g of solid) yield the analytically pure 3-(2-methylamino-l-hydroxyethyl)methanesulfonanilide methanesulfonate, 19.6 g (75%), M.P. 207-209°C. 

Reaction of 2,3-dihydrofuran with aryl triflate in benzene in the presence of a base and a palladium catalyst, prepared in situ from Pd(OAc)2 and 2 equivalents of (R)-BINAP, gave (R)-2-aryl-2,3-dihydrofuran (2) and a small amount of the regioisomer (5)-2-aryl-2,3-dihydrofuran (3) (Scheme 1). Table I demonstrates that the arylation reaction proceeds in extremely high enantioselectivity with a variety of aryl triflates. Particularly, almost enantiomerically pure (R)-2 was obtained with 2-naphthyl triflate and phenyl triflates bearing an electron-withdrawing substituent at the para or meta position. 

Although the selectivity of palladium catalysts in the hydrogenation of 1,5-COD is thus very high, the results also indicate that the hydrogenation of COE to cyclooctane (COA) does not cease after the maximum yield of COE has been attained. Hirai et al. studied the hydrogenation of 1,5-COD over a colloidal palladium catalyst, prepared by reduction of palladium(II) chloride in the presence of poly(iV-vinyl-2-pyrrolidone) in refluxing methanol with addition of sodium hydroxide, in methanol at 30°C and 1 atm H2, and obtained a mixture consisting of 0.4% 1,5-COD, 0.3% 1,4-COD, 97.8%... 

Agrell, J., Germani, G., Jaras, S.G., and Boutonnet, M. Production of hydrogen by partial oxidation of methanol over ZnO-supported palladium catalysts prepared by microemulsion technique. Applied Catalysis. A, General, 2003, 242 (2), 233. 

Alkylation of sodium 1-(alkoxycarbonyl)methyIphosphonates proceeds equally with acetates in THF from low to room temperature or in DME at reflux. The asymmetric allylic alkylation of the sodium diethyl l-(ethoxycarbonyl)methylphosphonate with 3-acetoxy-l,3-diphenyl-l-propene and cyclic allylic acetates in the presence of a chiral palladium catalyst, prepared from chiral phosphine and palladium acetate, in THF at room temperature proceeds in good yields (44-88%) and high ec s. ... 

Tanaka S., Mizukami F., Niwa S., Toba M., Tasi G., Kunimori K. Highly selective fomation of aldehydes in the hydrogenation of the corresponding acid chlorides with silica-supported palladium catalysts prepared by a complexing agent-assisted sol-gel method. Appl. Catal. A Gen. 2002 229 ... 

Lautens has spearheaded the study of a range of metal-catalyzed methods for the desymmetrization of various meso-oxabicyclooctanes [40]. In initial work, enantioselective nickel-catalyzed hydroalumination reactions of substrates such as 148 proved effective for the generation of cycloheptene 150 (95% ee, Scheme 14.24) [118], as also described in Section 7.5. The related desymmetrization reactions could be effected with carbon nucleophiles as well [119, 120], Thus, asymmetric ring-opening of 145 with Me2Zn mediated by a palladium catalyst prepared in situ with ligand 146 [121] led to the C3-C9 fragment (147) of the polyether antibiotic ionomycin (151) [120]. 

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