Palladium complexes reactions with carbon dioxide

Equations 1 to 3 show some of fixation reactions of carbon dioxide. Equations la and lb present coupling reactions of CO2 with diene, triene, and alkyne affording lactone and similar molecules [2], in a process catalyzed by low valent transition metal compounds such as nickel(O) and palladium(O) complexes. Another interesting CO2 fixation reaction is copolymerization of CO2 and epoxide yielding polycarbonate (equation 2). This reaction is catalyzed by aluminum porphyrin and zinc diphenoxide [3],... 

Sasaki Y, Inoue Y, Hashimoto H (1976) Reaction of carbon dioxide with butadiene catalysed by palladium complexes. Synthesis of 2-ethylidenehept-5-en-4-olide. J Chem Soc, Chem Commun 605-606... 

When applied to triple bonds, hydrocarboxylation gives a,p-unsaturated acids under very mild conditions. Triple bonds give unsaturated acids and saturated dicar-boxylic acids when treated with carbon dioxide and an electrically reduced nickel complex catalyst. Alkynes also react with NaHFe(CO)4, followed by CuCl2 2 H2O, to give alkenyl acid derivatives. A related reaction with CO and palladium catalysts in the presence of SnCE also leads to conjugated acid derivatives. Terminal alkynes react with CO2 and Ni(cod)2, and subsequent treatment with DBU (p. 1132) gives the a,p-unsaturated carboxylic acid. ... 

The parent methylenecyclopropane (16, R = H) as well as alkylidenecyclopropanes react with carbon dioxide under palladium(O) catalysis to yield furan-2(5//)-ones 17 and 18. Although a complex mixture of cyclotrimers, cyclotetramers and higher oligomers is obtained from the parent MCP, under optimized conditions with regard to the palladium/phosphorus ratio, polarity of the solvent, carbon dioxide pressure and reaction temperature, the [3-f2] cycloadduct 17 (R = H) can be obtained in 80% yield. 

Binger and Weintz studied the reaction of the unsubstituted methylene-cyclopropane with carbon dioxide and obtained the 3-methy1-2-buten-4-olide in yields up to 80 % [25,26]. As shown in Figure 10, parallel to the main reaction, the formation of cotrimers, cotetramers and copentamers can not be avoided. A mechanism is proposed, in which the palladium forms a trimethylenemethane intermediate which exists in two tautomeric structures (Figure 11). By insertion of carbon dioxide palladium carboxylate complexes are formed which release the furanone. 

As in the monoene chapter, the stoichiometric and catalytic reactions of dienes with carbon dioxide will be discussed in the sequence of the transition metal applied. It is remarkable, that almost the same metals are described both in monoene and in diene/C02 chemistry. Two differences, however, should be stressed In the presence of molybdenum and tungsten complexes no interactions between dienes and carbon dioxide are reported (until now). On the other hand, palladium is a much more versatile and effective metal in diene/C02 than in monoene/CO chemistry. 

CARBON DIOXIDE AS BUILDING BLOCK FOR FINE CHEMICALS SYNTHESIS Table 2 Reaction of carbon dioxide with butadiene Influence of the palladium complex ... 

Recently, acrylic acid methylester palladium complexes are able to react with carbon dioxide. The substituted compound with carbon dioxide affords formic acid by reaction with hydrogen at room temperatures. Therefore, the reaction is the fixation of carbon dioxide by palladium compounds. 

Inoue Y, Hibi T, Satake M, Hashimoto H (1979) Reaction of methylenecyclopropanes with carbon dioxide catalysed by palladium(O) complexes. Synthesis of five-membered lactones. J Chem Soc Chem Commun 982-982... 

We reasoned that such a decarboxylation step could also be employed in a redox-neutral cross-coupling reaction with carbon electrophiles. On this basis, we drew up a catalytic cycle that starts with an oxidative addition of aryl halides or pseudohalides to a coordinatively unsaturated palladium(O) species f (Scheme 5). The more weakly coordinating the leaving group X, the easier should be its subsequent replacement by a carboxylate. At least for X = OTf, the palladium(ll) carboxylate h should form quantitatively, whereas for X = halide, it should be possible to enforce this step by employing silver or thallium salts as species g. The ensuing thermal decarboxylation of the palladium(ll) intermediate i represents the most critical step. Myers results indicated that certain palladium(ll) carboxylates liberate carbon dioxide on heating. However, it remained unclear whether arylpalladium (II) carboxylate complexes such as i would display a similar reactivity. If this were to be the case, they would form Ar-Pd-Ar intermediates k, which in turn are... 

In contrast, reaction of allene with carbon dioxide in the presence of palladium or rhodium complexes affords a mixture of pyrones and esters. 

Palladium(II) complexes possessing bidentate ligands are known to efficiently catalyze the copolymerization of olefins with carbon monoxide to form polyketones.594-596 Sulfur dioxide is an attractive monomer for catalytic copolymerizations with olefins since S02, like CO, is known to undergo facile insertion reactions into a variety of transition metal-alkyl bonds. Indeed, Drent has patented alternating copolymerization of ethylene with S02 using various palladium(II) complexes.597 In 1998, Sen and coworkers also reported that [(dppp)PdMe(NCMe)]BF4 was an effective catalyst for the copolymerization of S02 with ethylene, propylene, and cyclopentene.598 There is a report of the insertion reactions of S02 into PdII-methyl bonds and the attempted spectroscopic detection of the copolymerization of ethylene and S02.599... 

A large number of heterogeneous catalysts have been tested under screening conditions (reaction parameters 60 °C, linoleic acid ethyl ester at an LHSV of 30 L/h, and a fixed carbon dioxide and hydrogen flow) to identify a suitable fixed-bed catalyst. We investigated a number of catalyst parameters such as palladium and platinum as precious metal (both in the form of supported metal and as immobilized metal complex catalysts), precious-metal content, precious-metal distribution (egg shell vs. uniform distribution), catalyst particle size, and different supports (activated carbon, alumina, Deloxan , silica, and titania). We found that Deloxan-supported precious-metal catalysts are at least two times more active than traditional supported precious-metal fixed-bed catalysts at a comparable particle size and precious-metal content. Experimental results are shown in Table 14.1 for supported palladium catalysts. The Deloxan-supported catalysts also led to superior linoleate selectivity and a lower cis/trans isomerization rate was found. The explanation for the superior behavior of Deloxan-supported precious-metal catalysts can be found in their unique chemical and physical properties—for example, high pore volume and specific surface area in combination with a meso- and macro-pore-size distribution, which is especially attractive for catalytic reactions (Wieland and Panster, 1995). The majority of our work has therefore focused on Deloxan-supported precious-metal catalysts. 

Tsuji and co-workcrs have shown that propargylic carbonate 22 oxidatively adds to the palladium(0) complex to provide an (alkoxo)palladium intermediate 23 with elimination of carbon dioxide [57]. Thus, the reaction of 22 with alkylboranes, 1-alkenyl-, 1-alkynyl-, and aiylboronic acids or their esters gives 24 in high yields under neutral conditions (Scheme 2-22) [50]. 

Addition of water to dienes is catalyzed by palladium complexes. The reaction has been used for synthesizing unsaturated alcohols and ethers from aliphatic conjugated C4 and Cg olefins 248). In particular, the hydration of butadiene with water in the presence of bis(2,4-pentane-dionato)palladium and triphenylphosphine gave 2,7-octadien-l-ol, l,7-octadien-3-ol, and 1,3,5,7-octatetraene 18). The reaction was accelerated by carbon dioxide. Compounds Pd(PPh3)4 and Pd(02C0)-(PPh3)2 were also effective. 

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