Palladium-chloride bond

In that complex, it may be that water reacts with the coordinated C2H4 to produce a cr-bonded CH2CH2OH group rather than an insertion reaction involving an OH group. The aldehyde is formed as H+ is lost, and the palladium is produced as shown in Eq. (22.31). The palladium chloride catalyst can be recovered (the price of palladium is almost 500/oz as this is written) by the reaction with CuCl2. 

The results suggest that once hydroalumination has occurred at one end of the diene, the course of the reaction at the other double bond is significantly affected by the alkylaluminum group, possibly due to chelation in which a palladium-chloride-aluminum bond is thought to be important. 

The nucleophilic attack of the water or hydroxide species takes place in an anti fashion i.e. the oxygen attacks from outside the palladium complex and the reaction is not an insertion of ethene into the palladium oxygen bond. This has been demonstrated in a model reaction by Backvall [4], The reaction studied was the Wacker reaction of dideuterio-ethene (cis and trans) in the presence of excess of LiCl, which is needed to form 2-chloroethanol as the product instead of ethanal. The latter product would not reveal the stereochemistry of the attack Note that all of the mechanistic work has been carried out, necessarily, on systems deviating in one aspect or another from the real catalytic one. The outcome depends strongly on the concentration of chloride ions [5],... 

Palladium catalysts resemble closely the platinum catalysts. Palladium oxide (PdO) is prepared from palladium chloride and sodium nitrate by fusion at 575-600° [29,30]. Elemental palladium is obtained by reduction of palladium chloride with sodium borohydride [27, 31], Supported palladium catalysts are prepared with the contents of 5% or 10% of palladium on charcoal, calcium carbonate and barium sulfate [32], Sometimes a special support can increase the selectivity of palladium. Palladium on strontium carbonate (2%) was successfully used for reduction of just y, (5-double bond in a system of oc, / , y, (5-unsaturated ketone [ii]. 

C(l) in 355 is in the oxidation state of an aldehyde or a ketone in 1-alkylated products. The necessary solvolytic attack of the enol carbamate double bond requires substoichio-metric amounts of a catalyst such as mercuric acetate or palladium chloride and one equivalent of acid (e.g. methanesulphonic acid) for binding the liberated diisopropylamine. 

Metal-Halogen Counpounds. One of the few examples of an olefin insertion into a metal-halogen compound has been reported by Tsuji. The reaction, which also supports the idea that sigma-bonded metal-carbon compounds are intermediates in the palladium chloride-olefin oxidation reaction, was the addition of carbon monoxide to the ethylene palladium chloride 7r-complex in nonaqueous solvents to produce a moderate yield of 3-chloropropionyl chloride (96). 

Palladium chloride bis(benzonitrile) reacts with allene probably by an insertion mechanism to produce 7r-2-chloroallylpalladium chloride dimer and products containing two allene units per palladium atom (84). It would appear that the palladium chloride addition to allene occurs both possible ways to one of the double bonds. Addition of the palladium to the terminal position would give a 7r-allyl... 

Treatment of 1-azirine (292) with catalytic quantities of dichlorobis(benzonitrile)pal-ladium(II) gave a quantitative yield of the indole (293) (77CC664). This transformation proceeds through the intermediacy of a 2 1 azirine-palladium chloride complex. Conversion of the 1-azirine ring to indoles under uncatalyzed thermolytic conditions provides a mechanistically interesting comparison with the Pd(II)-catalyzed conversions. The C—N bond cleavage in the latter is apparently accelerated as a result of the coordination of the azirine to palladium. 

Reactions with Acyl Halides. The palladium-carbon bond in alkyl VII and acyl VIII complexes also can be broken by acyl and alkyl halides, respectively, to give ketones (55). The reaction of the benzyl complex Vila with acetyl chloride in the presence of 2,6-lutidine provided good yield of methyl benzyl ketone, XVII. In the absence of the base, lower yields (26% ) were obtained. Surprisingly, a similar reaction between the benzyl complex and an excess of phenylacetyl chloride afforded a 156% yield of dibenzyl ketone, XVIII, based on the starting benzyl complex (see bottom of p. 105). 

A mixture of palladium chloride and triphenylphosphine effectively catalyzes carboxylation of linoleic and linolenic acids and their methyl esters with water at 110°-140°C and carbon monoxide at 4000 psig. The main products are 1,3-and 1,4-dicarboxy acids from dienes and tricarboxy acids from trienes. Other products include unsaturated monocar-boxy and dicarboxy acids, carbomethoxy esters, and substituted a,J3-unsaturated cyclic ketones. The mechanism postulated for dicarboxylation involves cyclic unsaturated acylr-PdCl-PhsP complexes. These intermediates control double bond isomerization and the position of the second carboxyl group. This mechanism is consistent with our finding of double bond isomerization in polyenes and not in monoenes. A 1,3-hydrogen shift process for double bond isomerization in polyenes is also consistent with the data. 

When either an alcohol or an amine function is present in the alkene, the possibility for lactone or lactam formation exists. Cobalt or rhodium catalysts convert 2,2-dimethyl-3-buten-l-ol to 2,3,3-trimethyl- y-butyrolactone, with minor amounts of the 8-lactone being formed (equation 51).2 In this case, isomerization of the double bond is not possible. The reaction of allyl alcohols catalyzed by cobalt or rhodium is carried out under reaction conditions that are severe, so isomerization to propanal occurs rapidly. Running the reaction in acetonitrile provides a 60% yield of lactone, while a rhodium carbonyl catalyst in the presence of an amine gives butane-1,4-diol in 60-70% (equation 52).8 A mild method of converting allyl and homoallyl alcohols to lactones utilizes the palladium chloride/copper chloride catalyst system (Table 6).79,82 83... 

Although these catalytic partial hydrogenations of alkynes may well be regarded as the procedure of choice for (Z)-alkenes,25 other catalytic systems have been explored. These include a sodium hydride-sodium alkoxide-nickel(n) acetate reagent,26 and a sodium borohydride-palladium chloride-polyethylene glycol system.27 Diisobutylaluminium hydride (DIBAL) has also been used for the conversion of alkynes into (Z)-alkenes.28 ( )-Alkenes are formed when the internal triple bond is reduced with sodium in liquid ammonia.29... 

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],... 

The preparation of organopalladium compounds by exchange reactions of palladium salts and organo-lead, -tin, or -mercury compounds is apparently not the only way that they can be obtained but it does seem to be the most useful way. Convincing evidence is now available to show that direct metalation of aromatic compounds with palladium salts (palladation) can occur. Since the initial report of Cope and Siekman 32> that palladium chloride reacted readily with azobenzene to form an isolable chelated, sigma-bonded arylpalladium compound, several additional chelated arylpalladium compounds have been prepared. 

Phenylation of a,/3-unsaturated ketones can be attained by reaction with phenylmercuric chloride or tetraphenyltin (usually 1.5 equivalents) catalyzed by an acidic solution of palladium chloride and tetrabutylam-monium chloride (57). The reaction is limited to substrates containing a disubstituted double bond such as 52 (i.e., cholest-4-en-3-one and 3,5,5-trimethyl-2-cyclohexen-l-one are inert). 

The palladium chloride complex of 1,5-cyclooctadiene is similarly prone to transannular bonding. A report by Chung and Scott described the smooth conversion of 46 to 47 at room temperature in the presence of lead tetraacetate.81 ... 

Hydrosilanes 398 react with carbodiimides in the precence of palladium chloride by insertion into the Si—H bond to give N-silylformamidines 399. ... 

Acylpalladium complexes are readily prepared through oxidative addition of Pd° complexes to acid chlorides. PdL4 compounds, where L is a tertiary phosphine, react with acid chlorides at room temperature to give trani-L2Pd(COR)Cl complexes. Since carbon monoxide does not insert into palladium acyl bonds, Pd(C0C02R) complexes are made from oxidative addition of oxalyl chloride monoesters. 

Aldehyde C-H bonds can also undergo cyclometalation with palladium salts. Reaction of 8-quinolinecarbaldehyde with PdCLt gives a chloride-bridged dimer with a palladium-acyl bond (equation 75). No intermediates could be isolated in case of the palladium reaction, but when [(PEt3)PtCl2]2 is reacted with 8-quinolinecarbaldehyde, a platinum complex is isolated with an intact aldehyde C-H bond. The nitrogen atom of the quinoline is coordinated to the platinum, and the aldehyde C-H bond occupies an axial site in the complex. Heating this material results in insertion into the aldehyde C-H bond and formation of a chelated platinmn acyl. 

Simple terminal alkenes or tranx-disubstituted alkenes gave good yields of the formal addition product when three equivalents of a secondary amine (dimethyl- or diethyl-, but not diisopropylamine) and bis(benzonitrilc)palladium chloride were used at low temperature, after reduction of the C-Pd bond. The yields were modest to very low with (Z)- or cyclic alkenes and using primary amines9, l0. 

Complex formation results in a downfield change in the chemical shift of the methyl protons and a decrease in the double-bond infrared stretching frequency from 1680 to 1532 cm h In the presence of a small excess of PdCl2, the complex is rapidly converted to hexamethylbenzene and palladium chloride. 

As seen from Table III, 77-tetraphenylcyclobutadienepalladium chloride serves as the cyclobutadienylating reagent. It is a specific reaction in that it is determined by the nature of the solvent. Ligand transfer proceeds satisfactorily only in hydrocarbons at elevated temperatures. The 77-ligand transfer can be accomplished either with metal carbonyls or their cyclo-pentadienyl derivatives, and with (R3P)2NiX2- Two different mechanisms have been proposed for this reaction 174). The first involves cleavage of the palladium-tetraphenylcyclobutadiene bond (a D-type mechanism). 

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