Nickel 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],... 

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. ... 

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). ... 

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. 

Already in 1977 Inoue discovered the reaction of hexynes with carbon dioxide catalyzed by nickel complexes [86]. 1-Hexyne reacted with CO2 in the presence of a nickel/dppe-catalyst to give the butyl-substituted pyrone in 50 % yield (Figure 31). As by-products the oligomers of 1-hexyne were formed. Similar reactions proved to be possible with alkynes containing internal double bonds, such as 3-hexyne and 4-octyne [87,88], giving tetrasubstituted pyrones. Yields up to 60 % could be obtained. 

There is now a growing literature of nickel organometallic complexes that contain carbon dioxide or related cumulene ligands that result from reactions with carbon monoxide. The first structurally characterized complex of carbon dioxide was the nickel complex Ni(G02)(PCy3)2 reported in 1975. A more recent study of this complex provides the complete assignments of the vibrational spectra and theoretical calculations of different isomers in support of a mechanism for CO2 fluxionality that involves end-on coordination. The tridentate pincer ligand 2,6-bis((diiso-propylphosphino)methyl)phenyl (PGP) has been used to form the square-planar Ni(ii) hydroxide complex Ni(OH)(PGP). The complex Ni(OH)(PCP) reacts with CO to give a binuclear /X-GO2 complex (Equation (2)). 

Schindler et al. carried out a kinetic analysis for the reaction of isoprene (ip) with carbon dioxide and Ni(bpy)(cod) [103]. Ni(bpy)(cod) did not react directly with CO2 (see also Sect. 5.2), but reacted reversibly with isoprene to give Ni(bpy)(ip). The kinetic results support a mechanism where, in a fast preequilibrium step, one of the bonds between Ni and cod is cleaved and, in a following step, ip coordinates to the free coordination site (Scheme 5.23). At low temperatures Ni(bpy)(ip) can further react, through a consecutive equilibrium, with another ip molecule to give Ni(bpy)(ip)2. However, in the presence of CO2, the nickel-ip complex, Ni(bpy)(ip), reacts irreversibly with the heterocumulene to form the product complex (3-5-q )-3-methyl-3-pentenylato)nickel bipyridine (Scheme 5.23). The activation parameters for the latter step were calculated to be A// = 25 7 kJ/mol and = 184 24 J/(mol K). The large negative activation entropy indicates that the carboxylation reaction proceeds in an associative way, during which CO2... 

Li J, Jia G, Lin Z (2008) Theoretical studies on coupling reactions of carbon dioxide with alkynes mediated by nickel(O) complexes. Organometallics 27 3892-3900... 

Inoue Y, Itoh Y, Kazama H, Hashimoto H (1980) Reaction of dialkyl-substituted alkynes with carbon dioxide catalyzed by nickel(O) complexes. Incorporation of carbon dioxide in alkyne dimers and novel cyclotrimerization of the alkynes. Bull Chem Soc Jpn 53 3329-3333... 

The reaction of Uganded nickel , molybdenumand niobium complexes with carbon dioxide produces [2+1] cycloadducts 11, which are relatively stable compounds. 

The reaction of alkynes with carbon dioxide in the presence of nickel (o) catalysts leads to the formation of metallacyclic 1 1 and 2 1 complexes. For example, the reaction of dimethylacetylene with carbon dioxide, in the presence of 1,5,9-cyclododecatrienenickel and Af,Af,A, Af-tetramethylenediamine, affords the five-membered ring metallacycle 20 in 65 % yield Hydrolysis of the metallacycle affords 2-methylcrotonic acid. 

Zirconium complexes of dienes react with carbon dioxide to give metallacycles, which also undergo reaction with another equivalent of carbon dioxide to give dicarboxylic acids after hydrolysis" . Oxidative coupling of dienes with carbon dioxide is also observed using nickel (o) catalysts" . 

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... 

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. 

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