Carbon dioxide complexes formation

Carbamoyl complexes from metal carbonyls and amines 5.8.2.12.4 Carbanions reactions with alkene complexes 5.8.2.3,4 metal carbonyls 5.8.2.S.5 Carbene complexes by alkene metathesis 5.8.2.3.11 formation 5.8.2.8.5 Carbides alkali metal formation 5.10.2.1 bonding 5.10.2 formation 5.10.2 industrial uses 5.10.2 interstitial formation 5.10.2 Carbometallacycle formation 5.S.2.2.2 Carbometallacycles from n-allyl complexes 5.S.2.3.9 Carbon reaction with alkali metals 5.10.2.1 Carbon dioxide complexes formation 5.8.2.14.1 Carbon monoxide displacement by alkenes 5.8.2.3.1 Carbonyl complexes by ligand exchange 5.8.2.12.2 from carbon monoxide 5.8.2.12.1, 5.8.2.12.2... 

In order to rationalize the orr/zo-selectivity observed in the reaction of sodium phenoxide 1 with carbon dioxide, the formation of a complex 3 is assumed. By that complexation the carbon dioxide becomes polarized, and its electrophilic character is increased. Complex 3 is of suitable geometry for reaction with the activated ort/zo-carbon center " ... 

Figure 8.8 Reduction of carbon dioxide with formate dehydrogenase and porphyrin complex using light energy [6h].

These complexes show an interesting chemistry, e. g. they undergo coupling with ethene to give zirconacyclopentane 71 or with water to give zirconoxane 72, or they can undergo insertion of carbon dioxide with formation of the complexes 73 and 74. In all of these reactions, the pyridine moiety is restored. With acids, complex 73 liberates the corresponding carbonic acids 75 or esters 76. 

CAMPHOS catalyst, asymmetric hydrogenation of a,p-unsaturated carboxlic acids, 25 107-109, 112 -carbon bond, COj insertion, 28 132-134 -carbon dioxide complex, coordination, 28 125, 126, 128 oxide formation, 28 27 as catalyst, 26 335... 

Carbon dioxide reacts with [Mo(N2)2(PMe2Ph)4] to produce not a carbon dioxide complex, but a carbonato-carbonyl, whose formation involves reductive disproportionation of C02 (equation 16). The structure of the Mo" product [ Mo(CO)(PMe2Ph)3 2( -C03)2] has been determined by X-ray structure analysis.166... 

Formation of Carbon Dioxide Complexes. As mentioned in the introduction, our initial interest in synthesizing the PCy3 complexes was in their potential for binding C02. However, except for the formation of peroxycarbonate and carbonato complexes from IrCl(02)(PCy3)2 (44), which is well-established chemistry for some platinum metal peroxide complexes (42) (but, to our knowledge, not with PCy3 systems), we have not been able to isolate any C02 complexes or even carbonate or bicarbonate species which are formed sometimes in the presence of adventitious water (16). 

Less attention has been paid, however, to C02 organometallic chemistry during the past decade. Whilst many reduction or coupling reactions are known to proceed in the presence of stoichiometric or catalytic amounts of transition metal complexes, very few examples remain where the formation of a metal-C02 complex has led to an effective, catalytic reduction reaction of C02. Carbon dioxide complex photoactivation also represents an attractive route to CO bond cleavage, coupled with O-atom transfer. However, progress in the area of C02 utilization requires a better understanding of the reaction mechanisms, of the thermodynamics of reaction intermediates, and of structure-reactivity relationships. 

The first step in the activation of carbon dioxide by transition metal compounds is the formation of a M-C02 complex, since it is through coordination that the electronic structure of this molecule, and hence its reactivity, can be substantially modified. Transition metal complexes containing carbon dioxide in its intact form have received considable attention in the last decade (Inone et al, 1982), mainly with the aim of finding model systems for the activation of C02 and subsequent transformation into organic chemicals of comercial interest (Aresta et al, 1987). Despite considerable and intensive work in this area, the number of structurally characterized carbon dioxide complexes is stilt very limited, and they have been found to contain side-on (Alvarez et al, 1986), 72 -coordinated and, l2 C-coordinated (Calabrese et al, 1983) C02. 

Biocatalytic synthetic reactions also include carbon dioxide fixation with the production of methanol in artificial multi-enzyme systems [188]. Formate dehydrogenase (FDH, EC 1.2.1.2) can catalyze the reduction of carbon dioxide to formate, and methanol dehydrogenase (MDH, EC 1.1.99.8) can catalyze the reduction of formate to methanol. Both of these enzymes require NAD+-NADE1 cofactor, and in the presence of the reduced dimethyl viologen mediator (MV+), they can drive a sequence of enzymatic reactions. The cascade of biocatalytic reactions results in the reduction of CO2 to formate catalyzed by FDEI followed by the reduction of formate to methanol catalyzed by MDH. A more complex system composed of immobilized cells of Parococcus denitrificans has been demonstrated for the reduction of nitrate and nitrite [189]. 

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 challenging photochemical reduction of carbon dioxide to formate is catalyzed by Ru" [111] (cf. Section 3.3.4). For example, with the 2,2 -bipyridine-ruthenium(II) complex the active species is formed by photolabilization. Water renders the system more efficient with quantum yields up to 15%. Methanol is the photoproduct when CO2 is reduced with Ti02 in propene carbonate/2-propanol... 

Treatment of FMC 55626 with triethylamine (Scheme 3) resulted in gas evolution, presumably carbon dioxide, and formation of complex reaction products. Although the components of this reaction have not been identified, the NMR spectrum did show a peak that could be assigned to the methine proton of an isobutyric acid. In the case of two primary amines (methylamine and aniline), cleavage of the acyl oxygen bond occurred to give the bis-amides 7. These amides are similar in activity to FMC 55626 and, like FMC 55626, are several times more active in autoclaved soils. 

The synthesis and coordination chemistry of carbon dioxide complexes has attracted a lot of attention over the years " and their reactivity, not surprisingly, includes several types of 1,2-migratoty insertion reactions. Thus, CO2 inserts into a variety of M-X bonds (X= H, C, O, N, P, S, Si) to yield the corresponding M-0C(0)X products, often following the initial formation of a Tt-complex (Scheme 10). 

Very related to the titanium chemistry described above are experiments with resembling molybdenocene complexes. If the molybdenum-diphenyl-acetylene complex Cp2Mo(PhC=CPh) is used as starting material, no C-C linkage reaction takes place with carbon dioxide. Instead, a crystalline solid was isolated whose x-ray proved the formation of a molybdenum-carbon dioxide complex [85] (Equation 15). 

Fixation of carbon dioxide and formaldehyde in their intact form on a metal centre is a primary goal in metal-promoted transformations of a C molecule, provided it forms metal-carbon bonds. Formation of formaldehyde and carbon dioxide complexes is, however, a quite rare reaction, in spite of the various strategies applied so far. On the contrary, coordination of dinitrogen has been found in a number of complexes all the mononuclear compounds so far identified prefer the end-on bonding mode. Activation of dinitrogen, however, can be much more pronounced in ca.se N2 binds the metal in a side-on fashion. 

Direct addition of CO2 across a Zr-Ir bond leading to stoichiometric reduction of carbon dioxide to formate was shown by Bergman and co-workers.[Gp2Zr(/t-NBu )IrCp ] 766 reacts rapidly with CO2 and heterocumulenes. Insertion of CO2 into an M-H bond, leading to a unique heterobimetallic formato complex and stoichiometric conversion of the formato complex to 766 and Li formate by addition of base, was also demonstrated. Different reactions gave the products listed in Scheme 109 and a possible mechanism for their formation was suggested. 

Scheme 11 Hydrogenation of carbon dioxide to formats by iridium(ni) trihydride PNP pincer complex 32...

Nozaki et al. applied the metal-ligand cooperation of Ir(III) PNP pincer complexes for the highly efficient catalytic hydrogenaticm of carbon dioxide to formats [83]. The chloroiriditim(ni) dihydride PNP complex 31 was synthesized by the reaction of [Ir(coe)2Cl]2 (coe = cyclooctene) with PNP ligand under hydrogen pressure. Reaction of complex 31 with excess of NaH resulted in the formation of stable Ir(III) trihydride PNP pincer complex 32 (Scheme 10). 

Trialkylborane additives promote the reduction of carbon dioxide to formate, via bis(diphosphine) Ni(II) and Rh(III) hydride complexes. Late transition metal hydrides, which can be formed by the reaction with molecular H2, transfer hydride to CO2 to yield a formate-borane adduct. In order to drive this process, the borane must be of appropriate Lewis acidity hence, weaker... 

Monsanto has disclosed the use of carbon dioxide—amine complexes which are dehydrated, at low temperatures, with phosphoryl chloride [10025-87-3] or thionyl chloride [7719-09-7] as a viable route to a variety of aUphatic isocyanates. The process rehes on the facile formation of the intermediate salt (30).REPLACEVariations of this process, in which phosgene is used as a dehydrating agent, have been reported earlier (84). Table 2 Hsts commercially available aUphatic isocyanates. 

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