Palladium-oxalate complexes

A likely mechanism for this reaction involves the nucleophilic attack of alcohol on two molecules of coordinated CO, followed by the coupling of the two palladium-bonded alkoxycarbonyl moieties (equation 179).438,451 jn support of this mechanism, the reaction of the bis(methoxycarbonyl) complex (143) with CO and PPh3 produces dimethyl oxalate and the reduced palladium(O) complex.451... 

Palladium forms complexes such as the dithio-oxalate ion, Pd(N2S2H)2, glyoximes, and phthalocyanine which are structurally similar to the compounds of Ni and Pt, and also numerous bridged compounds. Early X-ray studies established the planar trans configuration of (d) and (e) ... 

The precise mechanism in the catalyhc oxalate synthesis has not been established, hut it is likely that the catalytic process proceeds as shown in Scheme 1.35. The catalyhc cycle is comprised of nucleophilic attack of RO on the CO coordinated to Pd(II) to give an alkoxycarhonylpalladium(II) species, which further undergoes the similar CO coordinahon followed by external RO attack to give bis(alkoxycarbonyl)palladium(ll) complex [105,106]. Reduchve eliminahon of the two alkoxycarbonyl ligands to generate a Pd(0) species and its re-oxidahon are... 

For aU these oxalate syntheses, reaction intermediates are generally considered as palladium biscarboalkoxy complexes, since the reaction of PdX2L2 and CO in the presence of an alcohol and a base was known to give biscarboalkoxy palladium complex 12, which was thermally decomposed to give dimethyl oxalate 2a (Scheme 7).I2oh22]... 

Several Pd11 complexes with thiolate or thioether derivative ligands have been studied to be applied in the hydroxycarbonylation reaction.394 Aminothiolate complexes of palladium with PPh3 catalyze the conversion of styrene to 2-phenylpropionic acid in high yield and excellent regioselectivity.644 Under mild conditions and in the presence of a catalytic amount of an S, TV-chelated palladium or//zo-amino-arenethiolate complex, styrene reacts with CO and oxalic acid or water to selectively give 2-phenylpropanic aid in high yield.645... 

Under appropriate conditions, alcohols and amines can undergo an oxidative double carbonylation process, with formation of oxalate esters (Eq. 34), oxamate esters (Eq. 35) or oxamides (Eq. 36). These reactions are usually catalyzed by Pd(II) species and take place trough the intermediate formation of bis(alkoxycarbonyl)palladium, (alkoxycarbonyl)(carbamoyl)palladium or bis(carbamoyl)palladium complexes, as shown in Scheme 29 (NuH, Nu H = alcohol or amine) [227,231,267,293-300]. 

Dicarboxylic acids form monomeric complexes with palladium(II), K2[Pd(X2)2] (X2 = oxalate, malonate, etc,).153154 They may be prepared by warming a suspension of palladium(II) chloride with a concentrated solution of the alkali metal dicarboxylate or by using other palladium complexes containing readily substituted ligands such as [Pd(OH)2], [Pd(N03)2(H20)2] or [Pd(02CMe)2]3-155 These complexes are claimed to have useful antitumour properties.155 Complexes [Pd(X2)L2] (X2 = dicarboxylate L = amine or L2 = diamine) may be prepared by reaction of the dichloro complex with a carboxylate salt.156,128... 

Several groups have been successful at the catalytic conversion of carbon dioxide, hydrogen, and alcohols into alkyl formate esters using neutral metal - phosphine complexes in conjunction with a Lewis acid or base (109). Denise and Sneeden (110) have recently investigated various copper and palladium systems for the product of ethyl formate and ethyl formamide. Their results are summarized in Table II. Of the mononuclear palladium complexes, the most active system for ethyl formate production was found to be the Pd(0) complex, Pd(dpm)2, which generated 10/imol HCOOEt per /rniol metal complex per day. It was anticipated that complexes containing more than one metal center might aid in the formation of C2 products however, none of the multinuclear complexes produced substantial quantities of diethyl oxalate. 

Photochemistry of Oxalate and Dithiooxalate Complexes of Nickel, Palladium, and Platinum... 

This phosphine complex, however, is not reduced by alcohol to zero-valent palladium and oxalate ester, nor is it formed by insertion of carbon monoxide into the palladium-carbon bond of the related aikuxycarbonyl species. 

Whilst the platinum complex is not transformed either thermally or by addition of carbon monoxide into a Pt(0) species plus the oxalic ester, this transformation is quite easy for the corresponding palladium complex [23] ... 

Trifluorophosphine complexes of nickel, palladium, and platinum have been obtained by direct reaction of PF3 with the metal at elevated temperatures and pressures (172). Similarly several fluorophosphine complexes of zero-valent nickel can be made under very mild conditions (60°C) using metallic nickel formed by decarboxylation of nickel oxalate... 

Dicarboxylic acids form monomeric complexes with palladium(II), K2[Pd(X2)2] (X2 = oxalate, malonate, They may be prepared by warming a suspension of palladium(II)... 

Thermogravimetric curves for solid K2[Pd(C204)2],3H20 and other transition-metal oxalates indicate that the thermal stability of the anhydrous complexes decreases with increase in electron affinity of the central metal ion. AH values were obtained for both dehydration and decomposition. Subsequent studies showed carbon dioxide as the only gaseous product, the decomposition occurring via electron transfer from a 304 ligand to the central palladium. ... 

EDTA (ethylenediaminetetraacetic acid) forms stable metal chelates with a number of metal ions. Using this reagent as a complexing- agent, arsenic, bismuth, and selenium can be determined without any interference in the presence of nickel and cobalt. The cobalt-EDTA chelate is stable in 5 M HCl solution, whereas the corresponding bismuth complex is not. The influence of copper on the determination of arsenic can also be eliminated with EDTA, but not in the determination of selenium. Thiourea has been used to eliminate the influence of copper in the determination of antimony and sodium oxalate to eliminate the influence of copper and nickel in the determination of tin. An addition of thiosemicarbazide and 1,10-phenanthro-line reduces the interference of copper, nickel, platinum, and palladium in the determination of arsenic. 

Cobalt porphyrins have been used for several studies and exhibit catalytic activity ". For example when Co-tetraphenylporphyrin (5.15) and Co-octamethylporphyrin complexes are used, CO is obtained catalytically whereas palladium and silver porphyrins in DCL produced oxalate. However, demetallation of the complexes rapidly deactivates the catalyst ". In these cases, the catalytic process was interpreted in terms of the anion radical species of the reduced state of Pd (II) and Ag (II) porphyrins rather than the Pd(I) and Ag(I) states. ... 

More recently, Bouwman carried out a detailed study on the carbonylation of nitrobenzene in methanol with palladium bidentate phosphane complexes as catalysts [29-31]. After a careful analysis of the reaction, mixtures revealed that besides the frequently reported reduction products of nitrobenzene [methyl phenyl carbamate (MFC), A, 7/-diphenylurea (DPU), aniline, azobenzene (Azo) and azoxyben-zene (Azoxy)], large quantities of oxidation products of methanol were co-produced (dimethyl carbonate (DMC), dimethyl oxalate (DMO), methyl formate (MF), H2O, and CO). They proposed the Pd-imido species P2Pd = NPh, which is the central key intermediate that can link together all the reduction products of nitrobenzene and all the oxidation products of methanol into one unified mechanistic scheme. 

Fe4S4(SR)4] , are good catalysts for reduction of CO2. Recently it was found that other compounds also facilitate such reduction. Electrolytic reduction of CO2 in acetonitrile in the presence of [Rh(dppe)2]Cl leads to the formation of The rhenium(I) compound [ReCl(CO)3 (bipy)] catalyzes electrolytic reduction of CO2 to carbon monoxide. The electrolytic reduction of CO2 in some cases probably proceeds via the radical anion C02 its formation explains various reduction products see scheme (13.241). Palladium complexes, for instance, [Pd2Cl2(dppm)2], [Pd(dppm)2], and [PdCl2(dppm)], slowly catalyze reduction of CO2 to methane, ethyl formate, and traces of ethyl oxalate. 

PTFE increases the decomposition temperature of cadmium oxalate trihy-drate. Moreover, the products of cadmium complex degradation, in turn, increase the temperature at which an intensive degradation of PTFE begins. The thermal decomposition of the highly dispersed copper formate leads to the formation of a metal-polymer composition (20-34% Cu). The maximum on the nanoparticles granulometric composition curve corresponds to 4nm. No chemical interaction between the components was observed. The decomposition of a fine dispersion of palladium hydroxide in polyvinyl chloride (PVC) results in spatial structures with highly dispersed Pd particles (S = 26 m g ) in the nodes. This process increases in the temperature required for complete dehydrochlorination of PVC. The thermolysis of cobalt acetate in the presence of PS, PAA, and poly(methyl vinyl ketone) proceeds... 

Recently, new mononuclear and dinuclear palladium complexes containing one neutral and one anionic sulfur donor center derived from the atropisomeiic thiol-thioether derivative (RHbinas) were used as catalysts for the hydrocarboxylation of styrene in the presence of triphenylphosphine and oxalic acid. The new complexes are active catalysts for the hydrocarboxylation of styrene, showing a high regioselectivity toward the branched product (97%) under relatively mild conditions (Eq. 2). ... 

Double carbonylation of this type will mainly be dealt with here. The other type of processes introducing two adjacent carbonyl groups, such as production of oxalic acid derivatives catalyzed by palladium complexes, will also be treated here. The processes to... 

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