Palladium dichloride catalyst

Both pyrimidine and quinazoline derivatives have been investigated as ligands for palladium-mediated reactions. Examples of ligands prepared include the phosphine-free bipyrimidine 1181, which gave the isolable palladium dichloride catalyst 1182 <2001JOM(634)39>, and the chiral oxazolinyl-quinazoline BINAP analogs 1183 and 1184 <20060L5109>. 

Mizugaki et al. 74) have recently utilized thermomorphic properties of Pd(0)-complexed phosphinated dendrimers for dendritic catalyst recycling. Using the method developed by Reetz 16), they prepared dendritic ligands containing, respectively, 2, 8, 16, and 32 chelating diphosphines. Palladium dichloride was com-plexed to the dendrimers, and a reduction in the presence of triphenylphosphine gave the Pd(0)-complexed dendrimers (80—83). The dendritic complexes were active... 

A similar approach was taken for the synthesis of 45 by Miyaura. " Shaughnessy and Booth synthesized the water-soluble alkylphosphine 46, and found it to provide very active palladium catalysts for the reaction of aryl bromides or chlorides with boronic acids. The more sterically demanding ligand 47 was shown to promote the reactions of aryl chlorides with better results than 46. Najera and co-workers recently reported on the synthesis of di(2-pyridyl)-methylamine-palladium dichloride complexes 48a and 48b, and their use in the coupling of a variety of electrophiles (aryl bromides or chlorides, allyl chlorides, acetates or carbonates) with alkyl- or arylboronic acids very low catalyst loadings at Palladium-oxime catalysts 8a and 8b) have also been developed. In conjunction with... 

Dihaloazines also undergo carbonylation and, if the positional activation of the halogens is different, then the reaction might be carried out selectively. 2,3-Dichloro-5-(methoxymethyl)pyridine was, for example, selectively carbonylated in the 2-position in methanol in the presence of a bis(diphenylphosphino)palladium dichloride, dppb catalyst system under 15 atm CO (7.64.),83 The side product, present in less than 3% was the... 

The same reactions, carried out with potassium carbonate as base in place of a secondary amine, yield exocyclic dienes in good yield, although double-bond isomerization sometimes occurs (equation 38).93 Inclusion of tetra-zi-butylammonium chloride in the reaction mixture stops the double-bond isomerization. Thus, the reaction in equation (38) with the chloride yields only the bis(exomethylene) product in 45% yield in a slow reaction. Some N- and O-heterocyclic products, also, have been prepared by the intramolecular vinyl substitution reaction.94 A 16-membered ring lactone was made by the ring closure of a vinylic iodide group with a vinyl ketone group. The yield, based upon the reactant, was 55% but a stoichiometric amount of bis(acetonitrile)palladium dichloride was employed. The catalyst was prereduced with formic acid so that the reaction proceeded at 25 C (equation 39).95... 

In 2005 and 2006, Mori et al. reported the arylation of heterocycles with aryl iodides using palladium dichloride complexes as catalysts and silver nitrate or fluoride as activators (Scheme 10.50). The best coupling conditions were obtained with a combination of silver nitrate and potassium fluoride.82... 

Bis(triphenylphosphine)palladium dichloride [(Ph3P)2PdCl2] can also be used as a catalyst for the phase-transfer carbonylation of halides. However, considerably more drastic conditions [95°C, 5 atm] are required when compared with Co2(CO)8 (44). The carbonylation of allyl chlorides can be catalyzed by nickel tetracarbonyl, giving isomeric mixtures of bu-tenoic acids. There is evidence for the intermediacy of polynuclear nickel-ates in this phase-transfer process (45). Acetylene insertion did not occur... 

Transition-metal-catalyzed carbonylation of an iodide in the presence of an alcohol or water gives the ester or acid, respectively. Bis(triphenylphosphanyl)palladium dichloride and octa-carbonyldicobalt are efficient catalysts. Starting from diiodidc 16, dicarboxylic ester 17 or dicarboxylic acid 18 are obtained in good to excellent yield.The formation of 18 is a good alternative to the hydrolysis of an ester to an acid. ... 

In a finding of greater practical significance. Overman and coworicers showed that the reactions could be carried out with catalytic amounts of the palladium(II) complex, and that the catalytic effect was broadly applicable to acyclic 1,5-dienes as well7 In a typical example (equation 32), 2-methyl-3-phe-nyl-l,5-hexadiene rearranges in 1 h at room temperature in 87% yield in the presence of 0.06 equiv. of bis(benzonitrile)palladium dichloride, in contrast to the thermal rearrangement which has t n = 13 h at 177 °C. The cat yst thus provides an estimated rate acceleration of about 10 °. The product is a 93 7 mixture of ( )- and (Z)-isomers, corresponding to the equilibrium ratio. Palladium acetate and tetra-kis(triphenylphosphine) were ineffective as catalysts. One serious limitation is that the catalyzed reaction occurs only with those 1,5-dienes which possess an alkyl or aryl substituent at C-2 or C-5 (but not both). 

Very recently another reaction, which involves a palladium-catalyzed benzyl halide carbonylation step, has been commercialized by Clariant AG. Here, the carbonylation of 1,2-xylyl dichloride in the presence of a palladium-phosphine catalyst yields isochromanone (eq. (10)) [54]. 

It should also be noted that less-reactive chloroarenes can be carbonylated under biphasic conditions using bis(tricyclohexylphosphine)palladium dichloride as the metal catalyst. Again, the presence of a PT agent does not alfect the reaction... 

Two standard ways of catalyst preparation are considered. The first one proceeds through the precipitation of palladium hydroxide from palladium dichloride according to a simple method described in [8]. The support (1 g) is stirred with 15 ml of water. Palladium chloride (0.08 g) in 10% hydrochloric acid solution (5 ml) is added and the suspension is kept stirred during 15 minutes (pH is between 0 and 3). Then soda 20% (around 2.5 ml) is slowly added until pH reaches 12. Formaldehyde (2 ml) is added to reduce palladium hydroxide under stirring at constant pH value (pH = 12) for 1 h. The slurry is then heated to 90°C during 1 minute. pH is adjusted at 5, mbcture is rapidly cooled down, filtered and washed with water. ICP analysis of the filtrate is performed to ensure that the palladium is well on the support and to obtain an accurate value of metal loading of the catalyst. Catalysts prepared according to this method are called P catalysts. 

One can see from the data of Tab.4 that there is a small difference in catalytic properties of Pd/SAPO-31 samples prepared with different palladiiun salts. Slightly higher activity of the catalyst prepared with palladium dichloride may be related with a little bit higher pH value of the corresponding water solution what resulted in some hydrolysis of AlPO framework giving more hydroxyl groups and, finally, in higher dispersion of the metal [5]. 

The precursor aryl-malonamide 21 is prepared in a three-step procedure from 2,6-diethyl-toluidine. A technically feasible cross<oupling reaction has been developed for the synthesis of aryl malononitrile 20 starting from benzene derivative 19 and malononitrile. The optimized procedure with PdQ2/tricyclo-hexylphosphine and sodium tert-butoxide as base in refluxing xylene [81] was improved even further using palladium dichloride/triphenylphosphine as catalyst and sodium hydroxide as base in l-methyl-2-pyrrolidone at 125-130 °C [82]. The aryl-malononitrile 20 is hydrolyzed to the aryl-malonamide 21 in cone, sulphuric acid. 

The Sonogashira reaction allows for the direct cross-coupling of terminal alkynes with aryl halides under mild conditions through use of catalytic bis(triphenylphosphine)-palladium dichloride and Cul as the co-catalyst in the presence of an aliphatic amine. The formation of diphenylacetylene exemplifies the original Sonogashira reaction conditions ... 

Li this procedure, 0.5 mol% of palladium dichloride bis(acetonitrile) is added to neat acetoxy-acetal 82. The mixture is stirred for one hour at 50°C and then cooled to room temperature. Separation of the catalyst is achieved by short-path distillation under reduced pressure. The allylic acetate 83 is obtained as a 91 9 fE j-mixture in > 95% yield. 

This reaction has been modified to occur under microwave irradiation and using palladium dichloride as a catalyst. 

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