Nickel complexes carbon dioxide reactions

Pyridine compounds 45 can also be produced by the NHC-Ni catalysed cycloaddition between nitriles 43 and diynes 44 (Scheme 5.13) [16]. The SIPr carbene was found to be the best ligand for the nickel complex in this reaction. The reaction required mild reaction conditions and low catalyst loadings, as in the case of cycloaddition of carbon dioxide. In addition to tethered aUcynes (i.e. diynes), pyridines were prepared from a 3-component coupling reaction with 43 and 3-hexyne 23 (Scheme 5.13). The reaction of diynes 44 and nitriles 43 was also catalysed by a combination of [Ni(COD)J, NHC salts and "BuLi, which generates the NHC-Ni catalyst in situ. The pyridines 45 were obtained with comparable... 

Similar to the iron chemistry (compare Chapter 2.3), also nickel complexes allow the reaction of one molecule of butadiene with two molecules of CO2 yielding a,u-dicarboxylic acids [48]. In the reaction of butadiene and CO2 in the presence of nickelbis(cyclooctadiene) and tetramethylethylenediamine first a nickelamonocarboxylate is formed (Figure 19). By further treatment with carbon dioxide and by addition of pyridine a nickeladicarboxylate complex is obtained in yields up to 72 %. Decomposition of the complex with methanol/hydrochloric acid gives cis-dimethyl-3-hexenedioate. 

The [2-I-2-I-2] cycloaddition reaction of diynes 40 and carbon dioxide 41 were successfully catalysed by a NHC-nickel (Scheme 5.12) [15]. The NHC-Ni complex was prepared in situ from [NiCCOD) ] and two equivalents of carbene. Pyrones 42 were obtained in excellent yields at atmospheric pressure of CO and mild reaction conditions. 

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],... 

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 electrochemical incorporation of CO2 into perfluoroalkyl derivatives has been explored in the case of (perfluoroalkyl)alkyl iodides and (perfluoroalkyl)alkenes, with an electrochemical system based on the use of consumable anodes combined with organometallic catalysis by nickel complexes. Iodide derivatives have been functionalized to the corresponding carboxylic acids by reductive carboxylation. Interesting and new results have been obtained from the fixation of CO2 into perfluoroalkyl olefins. Good yields of carboxylic acids could be reached by a carefull control of the reaction conditions and of the nature of the catalytic system. The main carboxylic acids are derived from the incorporation of carbon dioxide with a double bond migration and loss of one fluorine atom from the CF2 in a position of the double bond. 

Aresta s conqrlex, (PCy3)2Ni[T) -(C,0)-C02], has been well studied for its physical and chemical properties. The ti -(C,0) coordination of carbon dioxide to the nickel con lex, (I Cy3)2Ni[Ti -(C,0)-C02], is fivored as a starting con lex with the ylide due to the electrophilic carbon of the coordinated CO2. The complex was first reported in 1974 ° l The reaction between the Aresta s carbon dioxide complex and an ylide provides the first exanqile of a Wittig Reaction on a coordinated carbon dioxide complex. 

There are two possible pathways to homologate methanol with carbon dioxide the CO2 insertion path and CO insertion path (Scheme 2). As for the former, Fukuoka et al. reported that the cobalt-ruthenium or nickel bimetallic complex catalyzed acetic acid formation from methyl iodide, carbon dioxide and hydrogen, in which carbon dioxide inserted into the carbon-metal bond to form acetate complex [7]. However, the contribution of this path is rather small because no acetic acid or its derivatives are detected in this reaction. Besides, the time course... 

Nickel(O) complexes undergo oxidative addition reactions with alkynes to give nickelacyclopentadienes and also react under certain conditions with carbon dioxide or isocyanates to form oxanickelacyclopentenones (87) " or azanickelacyclopentenones (88) (Scheme 30). In both cases the chelating basic ligand TMEDA (tetramethylethylenediamine) influences the reaction strongly. 

Ditertiary phosphane complexes of nickel were found to be effective in the formation of pyrone 108 by cyclocotrimerization of alkynes with carbon dioxide. The formation of the nickelacyclopentadiene 105 from two moles of alkyne and a nickel complex is followed by CO2 insertion into a nickel-carbon bond to give the oxanickelacycloheptadienone 106, which then eliminates 108 with intramolecular C—O coupling. Another route involving [4 + 2] cycloadditions of 105 with CO2 in a Diels - Alder reaction to give 107 cannot be ruled out but is less probable because CO2 does not undergo [4 + 2] cycloaddition with dienes. Addition of another alkyne to 105 results in the formation of a benzene derivative (Scheme 38). ... 

The abundant chemistry of Ni(CO>4 under reductive reaction conditions leading to the formation of dinuclear nickel complexes or even to nickel clusters suggests the involvement of higher aggregates, however. An overview of the reactivity of nickel complexes, and of Ni(CO)4 in particular, is given in a series of excellent reviews by Jolly [13]. There seems to be evidence of an autocatalytic cycle for the formation of the active catalyst [14]. Parallel to this, the water-gas shift reaction (eq. (5)) occurs, resulting in the formation of carbon dioxide and hydrogen, which is known to form metal hydrides in the presence of metal carbonyls [15]. 

Interaction between oxygen and carbon monoxide preadsorbed on NiO(10 Li)(250°) produces C03-(ads) ions, as in the case of all other samples. Thermochemical cycles 4 and 5 (Table XV) show, moreover, that the subsequent conversion of the complex ions by carbon monoxide yields carbon dioxide which remains partially adsorbed. Reaction mechanism II is therefore also probable on lithium-doped nickel oxides. 

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