Stoichiometric hydroformylation

Although Eq. (3) indicates that CO absorption is required for aldehyde formation, it has been shown by Karapinka and Orchin 18) that at 25° and with a moderate excess of olefin the rate of reaction and the yield of aldehyde are similar when either 1 atm of CO or 1 atm of Nj is present. Obviously CO is not essential for the reaction and a CO-deficient intermediate, probably an acylcobalt tricarbonyl, can be formed under these conditions. The relative rates of HCo(CO)4 cleavage of tricarbonyl and tetracarbonyl are not known, and thus the stage at which CO is absorbed in the stoichiometric hydroformylation of olefins under CO is not known with certainty. Heck (19) has shown conclusively that acylcobalt tetracarbonyls are in equilibrium with the acylcobalt tricarbonyl ... 

Essentially the same sequence of reactions was proposed (22a) to explain the isomerization of olefins which accompanies the stoichiometric hydroformylation of olefins. In particular, it has been suggested that the active catalyst is cobalt hydrotricarbonyl, which first adds by Markownikoff addition and is then eliminated in the opposite direction ... 

Karapinka and Orchin (18) made an extensive study of the isomerization of 1-pentene under stoichiometric hydroformylation conditions. 

Studies of stoichiometric hydroformylation, spectroscopic identification, isolation, and transformation of intermediates provided valuable information of the understanding of the catalytic reaction. Despite the complexity of the process, important conclusions were also drawn from kinetic studies. 

C and a total pressure of 1-300 atm (the pressure of the hydro-formylation reaction), depending on the reactivity of the olefin. After the cobalt carbonyl hydride has passed from the aqueous phase into the organic phase (Reaction 3), stoichiometric hydroformylation (6, 7, 8) takes place (Reactions 4-8). 

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 stoichiometric hydroformylation of olefins with cobalt hydrocarbonyl is also inhibited by an atmosphere of carbon monoxide (62, 73) (Section II, A) and this has been shown to involve a CO inhibition of alkylcobalt carbonyl formation (Eq. (18)). 

A useful study has just been completed by Roos and Orchin (125), who have examined the effect of ligands such as benzonitrile on the stoichiometric hydroformylation of olefins. A variety of such reagents (acetonitrile, anisole) were found to act in a similar manner to carbon monoxide by suppressing the formation of branched products and the isomerization of excess olefin. The yield of aldehyde was also increased by increasing ligand concentration up to 2 moles per mole of cobalt hydrocarbonyl. Benzonitrile was not found to affect the rate of the reaction of cobalt hydrocarbonyl with acylcobalt tetracarbonyl, so the ligand must have affected an earlier step in the reaction sequence. It seems most likely that cobalt hydrocarbonyl reacts with olefin in the presence of benzonitrile to form an acylcobalt tricarbonyl-benzonitrile complex which is reduced more rapidly than the acylcobalt tetracarbonyl. 

The stoichiometric hydroformylation of substituted olefins has already received sufficient discussion (Section II, A). Table I gives a list of references... 

SCHEME 4 SPO platinum catalysts. Top row stoichiometric hydroformylation with 1 middle row, catalyst 4 and hydrogen bond switching in 6 bottom row heterolytic cleavage of dihydrogen (69-71). (For a color version of this figure, the reader is referred to the Web version of this chapter.)... 

An alternate bimetallic pathway was also suggested, but not favored, by Heck and Breslow (also shown in Scheme 1). The acyl intermediate could react with HCo(CO)4 to undergo intermolecular hydride transfer, followed by reductive elimination of aldehyde to produce the Co-Co bonded dimer Co2(CO)s. A common starting material for HCo(CO)4-catalyzed hydroformylation, Co2(CO)g is well-known to react with H2 under catalysis reaction conditions to form two equivalents of HCo(CO)4. The bimetallic hydride transfer mechanism is operational for stoichiometric hydroformylation with HCo(CO)4 and has been proposed to be a possibility for slower catalytic hydroformylation reactions with internal alkenes.The monometallic pathway involving reaction of the acyl intermediate with H2, however, has been... 

When substituted cyclopropenes are treated with HCo(CO)4 or HMn(CO)5, aldehydes, aside from hydrogenation products, can be obtained in a stoichiometric hydroformylation process. When cyclopropene 3 is dissolved in hexane and treated with a twofold excess of HCo(CO)4 under a carbon monoxide atmosphere, the only aldehyde product observed is methyl l,2-cfs-2,3-/ranj-2-formyl-2,3-diphenylcyclopropane-l-carboxylate (4). It can be separated from the hydrogenation products and isolated from the reaction mixture by crystallization or chromatography. The major amount of hydrogenation products (88 /o) arises from cis addition of hydrogen to the double bond. A similar reaction has been observed when HMnfCO), rather than HCo(CO)4, is used. Thus, in both hydroformylation and hydrogenation, products arising from cis addition are predominantly or even exclusively formed (see Table 1). ... 

When substituted cyclopropenes are treated with HCo(C0)4 or HMn(CO)5, aldehydes, aside from hydrogenation products, can be obtained in a stoichiometric hydroformylation process.16... 

The prediction that tetracarbonylcobalt hydride would act as a catalyst in hydroformylation reactions 133, 224) has been amply verified for example, the stoichiometric hydroformylation, using HCo(CO)4, of 1-pen-tene at room temperature affords a variety of isomeric aldehydes 187). Also, HCo(CO)4 is formed under the high pressure (100 atm. 1 1 H2 CO) and temperature (100°-300°C) conditions of the hydroformylation reaction 183, 226). 

Stoichiometric hydroformylation of a polyolefin iron complex was reported by loset and Roulet [8], which preferentially afforded the ewrfo-formyl isomer together with the hydrogenation product (Scheme 1.60). 

Scheme 6.108 Formation of dimerization products in the stoichiometric hydroformylation of...

TE Nalesnik, M Orchin. Stoichiometric hydroformylation with HMn(CO)5. J Organomet Chem 222 C5-C8, 1981. 

The stoichiometric hydroformylation of allyldiphenylphosphine with RhH(CO>2(PR3) (PR3 is a bulky phosphine) allowed the preparation of several rhodacycles [236, 237, 238, and 239], which were characterized and gave some light on the reaction intermediates in rhodium-catalyzed hydroformylation. ... 

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