Hydrocarboxylative dimerization

Based on the DFT calculations, a plausible catalytic cycle has been proposed for the Ru-catalysed hydrocarboxylative dimerization of phenylacetylene PhC=CH with AcOH, which affords (l , 3 )-l,4-diphenyl-l,3-butadienyl acetate. The calculations shed light on the impact of the substituents of the alkyne and carboxylic acid substrates and the effect of solvents on the catalyst efficiency. 

The dimer acids [61788-89-4] 9- and 10-carboxystearic acids, and C-21 dicarboxylic acids are products resulting from three different reactions of C-18 unsaturated fatty acids. These reactions are, respectively, self-condensation, reaction with carbon monoxide followed by oxidation of the resulting 9- or 10-formylstearic acid (or, alternatively, by hydrocarboxylation of the unsaturated fatty acid), and Diels-Alder reaction with acryUc acid. The starting materials for these reactions have been almost exclusively tall oil fatty acids or, to a lesser degree, oleic acid, although other unsaturated fatty acid feedstocks can be used (see Carboxylic acids. Fatty acids from tall oil Tall oil). 

The hydrocarboxylation of conjugated dienes such as butadiene can yield monocarboxylate, dicarbox-ylate or diene dimerized carboxylated products. The carboxylation reaction is important because it is a potential route to adipic acid. 

Palladium catalysts that are free of halide ions effect the dimerization and carboxylation of butadiene to yield 3,8-nonadienoate esters. Palladium acetate, solubilized by a tertiary amine or an aromatic amine, gives the best yields and selectivities (equation 57).87 Palladium chloride catalyzes the hydrocarboxylation to yield primarily 3-pentenoates.88 The hydrocarboxylation of isoprene and chloroprene is regio-selective, placing the carboxy function at the least-hindered carbon (82% and 71% selectively) minor amounts of other products are obtained (equation 58). Cyclic dienes such as 1,3-cyclohexadiene and 1,3-cyclooctadiene are similarly hydrocarboxylated. 

Transition metal catalyzed asymmetric hydrocarboration reactions are addition reactions forming one C—C and one C—H bond. Prominent examples are hydrovinylation, hydroformylation, hydroacylation, hydrocarboxylation, and hydrocyanation. Various related conversions, such as hydroalkylation, hydroarylation, conjugate addition, reductive dimerization, and metal induced ene reactions are collected in Section 1.5.8.2.6. dealing with miscellaneous methods of this type. Some of these methods are not exclusively mediated by metal catalysts and therefore are also covered in other sections of this volume. 

Interestingly, these hydrocarboxylation reactions also occur to some extent in metal-free systems, but the reaction efficiency can be improved significantly by the use of metal catalysts or promoters [18]. Among the variety of different transition metal catalysts, multicopper(II) compounds were usually the most active ones [18, 20], leading to product yields that are circa two to five times superior to those in the metal-free systems. The water-soluble tefracopper(II) complex [Cu4(/x4-0)(/u,3-tea)4 ( u,3-BOH)4][BF4]2 (6) was formerly used as a model catalyst in the hydrocarboxylations of C2-Q alkanes [18, 31]. Since then, the reactions have been optimized further [19-21] and extended to other alkanes and multicopper catalysts, namely including the dimer 2 [22], the trimer 5 [13], the tetramer 7 [14], and the polymers 11 [12], 12 [12], 13 [14], and 15 [15] (Table 3.1). Interestingly, in contrast to alkane oxidation, the hydrocarboxylation reactions do not require an acid cocatalyst. 

In the previous chapters we discussed alkene-based homogeneous catalytic reactions such as hydrocarboxylation, hydroformylation, polymerization, and oligomerization. In this chapter we discuss a number of other homogeneous cataljTic reactions where an alkene is the only or one of the principal reactants. Some of the industrially important reactions that fall under the former category are selective di-, tri-, and tetramerization of ethylene, dimerization of propylene, and di-and trimerization of butadiene. 

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