Carboxylation, of olefins

Coupling between ethene and CO2 can also be induced by Fe(0) complexes [26]. Remarkably, these systems can promote ethylene coupling with two CO2 molecules, affording a dicarboxylate which was esterified by means of acid hydrolysis in methanol. The nature of the ancillary ligands had a marked influence on the product distribution. In the presence of PMeg, methyl malonate was obtained 

More recently, the mechanistic details of nickel(0)-assisted oxidative coupling of CO2 with C2H4 have been studied by Papai et al. by means of density functional calculations [32]. The basic question addressed in this theoretical study was whether the intermediacy of a carbon dioxide complex is a general requirement in CO2-C2H4 coupling reactions. The calculations have been carried out for the model reaction (5.4), and have shown that this reaction is initiated by the addition 

Catalytic synthesis of acrylic acids by direct coupling of olefins with CO2 has attracted the interest of chemists since the early 1980s. Nevertheless, to date, this 

Nevertheless, metal-hydrido-acrylate species can be more straightforwardly obtained from ethene and CO2 by suitably changing the metal center. Carmona et al. found that a few Mo and W complexes possessed very similar chemistry and promoted the coupling of ethene and CO2, affording dimeric (Mo, W) or monomeric (W) hydridoacrylate complexes which, unfortunately, were unable to eliminate acrylic acid (Structure 5.2) [40,41]. For instance, in diethyl ether, flie reactions 

The observation of (triphos)Mo(C2H4)(C02) on the path to C-C bond formation between CO2 and ethene provides the first experimental evidence that simultaneous coordination of both ethene and carbon dioxide at a metal center is a prerequisite for coupling the two unsaturates. This behavior is somewhat different from what was described to occur at nickel centers (see above). It cannot be excluded that the requirement of precoordination of both CO2 and olefin, although being less stringent for late transition metal centers such as Ni, may likely be general for early transition metal centers. 

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The oxidative carboxylation of olefins appears to be a very interesting synthetic methodology for synthesizing CCs, starting from cheap and easily available reagents such as C02 and 02 (Equation 7.16). 

The direct oxidative carboxylation of olefins has great potential, and many advantages. Notably, it does not require the C02 to be free of dioxygen this is an especially attractive feature, as the cost to purify C02 is extremely high, and may discourage its use. Moreover, the direct oxidative carboxylation of olefins can couple two processes-the epoxidation of olefins, and the carbonation of epoxides. Hence, the process makes direct use of those olefins that are available commercially at low price, and which represent an abundant feedstock. Such an approach also avoids having to isolate the epoxide. 

A study of the photoaddition of formamide to olefins was undertaken with the aim of finding a new process for converting olefins to higher amides and possibly further to amines by reduction or by the use of the Hofmann rearrangement. Since hydrolysis of the amides to the corresponding carboxylic acids can be effected by standard procedures, this reaction provides a new process for carboxylation of olefins under mild conditions at room temperature. A similar reaction has been shown to take place in a thermal process, using peroxides as initiators (60). 

Koch-Haaf earboxylation This acid is much superior to the previously used 95 % H2SO4 for carboxylation of olefins, alcohols, and esters with CO at atmospheric pressure. The beneficial effect appears to be the higher solubility ol CO in this acid. 

The Ni-catalyzed electrocarboxylation of differently activated olefins has been reported to afford selective CO2 incorporation via hydrocarboxylation [11]. However, no CO2 incorporation occurred with non-activated alkenes such as 1- or 4-octene. Carboxylation of olefins 3 and 4 should give some indication on the influence of the Rp substituent on the double bond. 

Phosphates and phosphinates are also recommended as ligands. (R)- or (S)-Binaphthol phosphates 3.54 are used in palladium-catalyzed asymmetric hydro-carboxylation of olefins [923] or in rhodium-catalyzed cycloadditions of diazo compounds to olefins, albeit with modest selectivities in the latter case [924], Seebach and coworkers [925] tested phosphinates and phosphites prepared from diol 2.50 (R = R = Me, Ar = Ph) as ligands for rhodium and palladium in various enantioselective metal-catalyzed reactions [925], Rhodium-catalyzed hydrosilyla-tions of arylmethyl- or ethylketones by Ph2SiH2 were the only interesting reactions with these ligands. 

This is actually a crucial step in the carboxylation of olefins (Reppe reaction) with transition metal carbonyl catalysts Apart from these extreme cases, however, metal-carbon a-bonds as well as metal-hydride bonds are best described as moderately polarized covalent bonds, with negative charge on the carbon or hydrogen respectively ... 

The cleavage is a crucial step in the catalytic carboxylation of olefins because the formation of HCo(CO)4 permits continuation of the catalyst cycle. Olefin addition gives RCo(CO)4 which is then carbonylated to the acyl compound. 

Oxidative Carboxylation of Olefins to Afford Cyclic Carbonates... 

The direct oxidative carboxylation of olefins [108-110] couples two processes, namely (1) the epoxidation of the olefins and (2) the carbonation of the epoxide, occurring in the same reactor. Interestingly, it has been shown that CO2 modulates the oxidant properties of O2 [111]. 

Aresta M, Dibenedetto A (2002) Carbon dioxide as building block for the synthesis of organic carbonates behavior of homogeneous and heterogeneous catalysts in the oxidative carboxylation of olefins. J Mol Catal 182-183 399-409... 

Aresta M, Dibenedetto A, Tommasi I (2000) Direct synthesis of organic carbonates by oxidative carboxylation of olefins catalyzed by metal oxides developing green chemistry based on carbon dioxide. Appl Organomet Chem 14 799-802... 

Therefore, the direct synthesis of cyclic carbonates from olefins instead of epoxides, a so-called one-pot "oxidative carboxylation" of olefins, would be appealing. The oxidative carboxylation synthesis from olefins can be roughly viewed as the coupling of two sequential processes of epoxidation of olefins and CO2 cycloaddition to epoxides formed (Scheme 18). The reaction uses easily available and low-priced chemicals of olefins as substrates and, moreover, preliminary synthesis and separation of epoxides would be avoided. So, the oxidative carboxylation would be a simpler and cheaper carbonate synthesis process with industrial potential from environmental and economic points of view. Although the three-component couplings have been known at least since 1%2 [66], up to date, only a few works have been made on these reactions in contrast to extensive studies on the addition reactions of CO2 to epoxides in ILs as catalyst/or solvent. 

The oxidative carboxylation of olefins to cyclic carbonates can proceed through the first step of epoxidation of olefins and the subsequent cycloaddtion of CO2 to epoxides formed (Scheme 18). Thus it is supposed that a system of combining catalysts effective for the first step and for the second one would be effective for the direct synthesis of cyclic carbonates via the oxidative carboxylation of olefins. Indeed the direct preparation of carbonates was successfully achieved with a few catalyst systems including ILs coupled with oxidation catalysts. One patent [66] reported that the cyclic carbonate was formed from an olefin, CO2, and oxygen in the presence of dual catalysts. The catalyst system includes a heavy metal compound and a quaternary ammonium hydroxide or haUde. However, the heavy metal compounds would easily induce the corrosion of equipments and result in the undesired reduction of activity and selectivity. 

Scheme 23. Proposed mechanism of aerobic oxidative carboxylation of olefins catalyzed by Ru(TPP)(0)2/IL. X = I-, Br-...

In this chapter, we discuss theoretical studies of some selected transition metal-catalyzed reactions of carbon dioxide to illustrate how important concepts and insights can be derived as a result of these studies. These selected reactions include hydrogenation of CO2 with Hj, coupling reactions of COj and epoxides, reduction of CO2 with organoborons, carboxylation of olefins with COj, and hydrocarboxy-lation of olefins with CO2 and Hj. They are fundamentally important reactions of carbon dioxide and have been intensively investigated experimentally and theoretically. This chapter is not intended to be a comprehensive review. Instead, we discuss the above-mentioned selected examples that we believe to be representative and important in the area of homogeneous catalysis of COj by transition metals from our own perspective. 

In this chapter, we have reviewed theoretical studies of selected transition metal-catalyzed transformation of CO2 (i) hydrogenation of CO2 with H2 (ii) coupling reactions of CO2 and epoxides (iii) reduction of CO2 with organoborons (iv) carboxylation of olefins with CO2 and (v) hydrocarboxylation of olefins with CO ... 

Figure 11 Scope and limitations of base (A) and substrate (B) for the catalytic one-pot carboxylation of olefins with CO2.

Huguet N, Jevtovikj I, Gordillo A, et al. Nickel-catalyzed direct carboxylation of olefins with CO2 one-pot synthesis of a, -unsaturated carboxyhc acid salts. Chem Eur J. 2014 20 16858-16862. 

Aresta, M. Dibenedetto, A. Tommasi, I. Direct Synthesis of Organic Carbonates by Oxidative Carboxylation of Olefins Catalyzed by Metal oxides Developing Green Chemistry Based on Carbon Dioxide. Appl Organomet. Chem. 2000,14,799-802. Eghbali, N. Li, C.-J. Conversion of Carbon Dioxide and Olefins into Cyclic Carbonates in Water. Green Chem. 2007, 9, 213-215. 

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