Alkenes hydrocarbonylation

Carbonylation reactions have been observed using both Pd(II)-alkene complexes and CT-bonded Pd(II) species formed by oxidative addition. Under reductive conditions, the double bond can be hydrocarbonylated, resulting in the formation of a carboxylic acid or ester.238 In nucleophilic solvents, the intermediate formed by solvopalladation is intercepted by carbonylation and addition of nucleophilic solvent. In both types of reactions, regioisomeric products are possible. 

Esters can be formed when the hydrocarbonylation reaction is carried out in an alcohol.242 Although hydrocarbonylation is the basis for conversion of alkenes to carboxylic acids on an industrial scale, it has seen only limited application in laboratory synthesis. 

Olefin hydrocarbonylation can be used in conjunction with oxidative addition to prepare indanones and cyclopentenones, but the reaction is limited to terminal alkenes.243... 

Also referred to as the oxo process or hydrocarbonylation, hydroformylation is a route to producing an aldehyde from an alkene, hydrogen, and carbon monoxide. This process has been known for approximately 70 years, and it is still economically important because useful compounds are produced in enormous quantities by this means. The reaction is summarized by the following equation ... 

Rhodium (I) complexes of chiral phosphines have been the archetypical catalysts for the hydrocarbonylation of 1-alkenes, with platinum complexes such as (61) making an impact also in the early 1990s[1461. More recently, rhodium(I)-chiral bisphosphites and phosphine phosphinites have been investigated. Quite remarkable results have been obtained with Rh(I)-BINAPHOS (62), with excellent ee s being obtained for aldehydes derived for a wide variety of substrates1 471. For example, hydroformylation of styrene gave a high yield of (R)-2-phenylpropanal (94% ee). The same catalyst system promoted the conversion of Z-but-2-ene into (5)-2-methylbutanal (82% ee). 

Reactions of Alkenes and Alkynes in Presence of Metal Carbonyls. Metal carbonyls—e.g., Ni(CO)4, Fe(CO)5, and Co2(CO)s—and hydrocarbonyls— HCO(CO)4 and H2Fe(CO)4—act as catalysts for the transformation of simple unsaturated materials into a wide variety of larger molecules. Perhaps the simplest example is that of hydroformylation (Equation 7). Reppe chemistry... 

The hydroformylation of alkenes generally has been considered to be an industrial reaction unavailable to a laboratory scale process. Usually bench chemists are neither willing nor able to carry out such a reaction, particularly at the high pressures (200 bar) necessary for the hydrocarbonylation reactions utilizing a cobalt catalyst. (Most of the previous literature reports pressures in atmospheres or pounds per square inch. All pressures in this chapter are reported in bars (SI) the relationship is 14.696 p.s.i. = 1 atm = 101 325 Pa = 1.013 25 bar.) However, hydroformylation reactions with rhodium require much lower pressures and related carbonylation reactions can be carried out at 1-10 bar. Furthermore, pressure equipment is available from a variety of suppliers and costs less than a routine IR instrument. Provided a suitable pressure room is available, even the high pressure reactions can be carried out safely and easily. The hydroformylation of cyclohexene to cyclohexanecarbaldehyde using a rhodium catalyst is an Organic Syntheses preparation (see Section 4.5.2.5). 

The reaction of alkenes (and alkynes) with synthesis gas (CO + H2) to produce aldehydes, catalyzed by a number of transition metal complexes, is most often referred to as a hydroformylation reaction or the oxo process. The discovery was made using a cobalt catalyst, and although rhodium-based catalysts have received increased attention because of their increased selectivity under mild reaction conditions, cobalt is still the most used catalyst on an industrial basis. The most industrially important hydrocarbonylation reaction is the synthesis of n-butanal from propene (equation 3). Some of the butanal is hydrogenated to butanol, but most is converted to 2-ethylhexanol via aldol and hydrogenation sequences. 

The treatment of a cobalt(II) salt with synthesis gas generates sequentially Co2(CO)8 then HCo(CO>4. This catalyst is generated only at 120-140 C for the carbonylation to proceed smoothly 200-300 bar is required to stabilize the catalyst. If the hydridocobalt catalyst is prepared separately and then introduced into the reaction, temperatures as low as 90 C can be used for the hydrocarbonylation. An important consideration in industrial reactions is the normal to branched nib ratio to give the desired straight chain aldehyde, the hydridocobalt catalyst providing an nib ratio of -4 in the hydroformylation of propene under the lower temperature conditions. This catalyst will stoichiometrically hydroformylate 1-alkenes under ambient conditions. 

The kinetics of the Rh4(CO)i2-catalysed hydroformylation of 2-butenes are consistent with a mechanism involving fragmentation of the catalyst to the active mono- and nonactive bi-nuclear Rh-complexes. Interaction of the monomeric HRh(CO)3 with alkene appears to be the rate-limiting step. Binuclear Rh-complexes, predominating in the reaction mixture, serve as a reserve for the active monomeric complexes472. Amine-directed, Rh(I)-mediated hydrocarbonylation has been reported (347 —> 348)473. 

Addition of H and CO to alkenes and alkynes catalysed by transition metal complexes is called hydrocarbonylation, and is useful for the syntheses of carboxylic acids, their esters, aldehydes and ketones [1]. Oxidative carbonylation of alkenes and alkynes with Pd(II), treated in Section 11.1.5, differs mechanistically from hydrocarbonylation. Some carbonylation reactions occur at under 1 atm or low pressures, without using a high-pressure laboratory apparatus. Several commercial processes based on hydrocarbonylation have been developed. 

Formation of ketones via hydroacylation can be achieved either via transition metal catalyzed hydrocarbonylative coupling of two alkenes ... 

Hydrocarbonylative coupling of alkenes and alkynes is a modification of hydroformylation and gives ketones1-3. 

Production of the other lower carbon number products needed to produce the activity curve shown in Figure 2 would require the olefinic products from Reaction (4) to also participate in hydrocarbonylation as shown in Equation (4) for ethene in this view it would be necessary for the relative contribution of Reaction (4) to decrease with carbon number of the alkene and to become essentially zero for C5 and higher carbon number olefins. 

Nitrate radicals also react with alkenes by addition, which results in a variety of different compounds such as hydroxynitrates, nitrohydroperoxides and hydrocarbonyls (Wayne et al. 1991). 

Hydrocarbonylation of alkenes to give the saturated esters 136 and 137 is catalyzed by Pd(0) (see Chapter 8.1) [56]. It should be pointed out that the hydrocarbonylation is clearly different mechanistically from the oxidative carbonylation, which is promoted by Pd(II) to produce 130, 132 and 134. 

Cyclohydrocarbonylation (CHC) is the hydroformylation of a functionalized olefin followed by concomitant intramolecular nucleophillic attack to the newly formed aldehyde moiety leading to a cyclized product. As a variant, the CHC reaction also includes an intramolecular cascade process involving the hydrocarbonylation of a functional alkene, generating an acyl-metal intermediate, which undergoes an intramolecular nucleophilic attack to give the corresponding cyclic compound. CHC reactions have been developed into sophisticated cascade reactions forming bicylic and polycyclic compounds. ... 

The catalytic hydrocarbonylation and hydrocarboxylation of olefins, alkynes, and other TT-bonded compounds are reactions of important industrial potential.Various transition metal complexes, such as palladium, rhodium, ruthenium, or nickel complexes, have widely been used in combination with phosphines and other types of ligands as catalysts in most carbonylation reactions. The reactions of alkenes, alkynes, and other related substrates with carbon monoxide in the presence of group VIII metals and a source of proton affords various carboxylic acids or carboxylic acid derivatives.f f f f f While many metals have successfully been employed as catalysts in these reactions, they often lead to mixtures of products under drastic experimental conditions.f i f f f In the last twenty years, palladium complexes are the most frequently and successfully used catalysts for regio-, stereo-, and enantioselective hydrocarbonylation and hydrocarboxylation reactions.f ... 

Hydrocarbonylation of alkenes in alcohol is catalyzed by Pd(0) to give esters, and the reaction is expected to proceed via acylpalladium intermediates. Also, the acylpalladium... 

Moreover, it cannot be decided from the data available so far whether a dissociative mechanism (similar to that proposed by Heck and Breslow for the hydroformylation with HCo(CO)4 according to scheme 1) or rather an associative attack of the alkene on the hydrocarbonyl according to scheme 2 [929, 1039] is followed (see page 26). 

Dicobalt octacarbonyl is employed as a catalyst precursor in the hydrocarbonylation of alkenes to produce aldehydes. 

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