Hydrocarbonylation of olefins

Figure 2. Models for the transition states controlling asymmetric induction in the hydrocarbonylation of olefins...

Besides hydrocarbonylation of olefins with carbon monoxide, hydroacylation can also be achieved by addition of aldehydes to olefins in the absence of carbon monoxide. This reaction is usually induced by rhodium complexes, mainly of the Wilkinson s catalyst type. Other catalysts are also active, e.g., systems derived from ruthenium complexes. Hydroacylation via aldehyde addition reactions has only rarely been surveyed24. 

The data in Figure 2 appear to be consistent with that expected for a competitive mechanism in which one of the reactions is the typical FTS reaction and the other is a hydrocarbonylation of olefins. Thus, the added ethene-[l- C] would react according to two mechanisms ... 

These reactions provided the basis for the mechanistic understanding of such industrially important reactions as the hydrocarbonylation of olefins and the then recently discovered Ziegler-Natta polymerization. They held out promise of more useful catalyses and led to a flourishing activity in the area of organotransition metal chemistry world-wide during the 1960s and 1970s. 

Hydroformylation, or the 0X0 process, is the reaction of olefins with CO and H9 to make aldehydes, which may subsequently be converted to higher alcohols. The catalyst base is cobalt naph-thenate, which transforms to cobalt hydrocarbonyl in place. A rhodium complex that is more stable and mnctions at a lower temperature is also used. 

The Allylic Exchange of RCHaCH with HCo(CO)4 A second scheme for the isomerization of olefins by HCo(CO)4 consists of an exchange of an allylic hydrogen of the olefin with the hydrogen of the hydrocarbonyl through a six-membered transition state 18) ... 

Several related reations are summarized in Scheme 4.13. When a nucleophilic OH or NH2 group exists at the proper position of the olefinic substrate, cyclohy-drocarbonylation provides a lactone or a lactam. Allyl alcohols" " and homoallyl amines are converted into y-lactones and 8-lactams in high enantiomeric excesses. Thiol is employable as a nucleophile for hydrocarbonylation of a C—C double bond. A successful catalytic carbonylation is reported for hydrothiocarbonylation. ... 

This review deals with the recent developments in the transition metal-catalyzed carbonylation reaction, especially hydroformylation, hydrocarbonylation, and oxidative hydrocarbonylation reactions of olefins, referring to literature since 1994. Because of the importance of carbonyl functionality in organic chemistry and the ideal atom efficiency of... 

The addition of cobalt hydrocarbonyl to olefins has been investigated and information on the detailed mechanism of the reaction obtained. The reaction of 1-pentene with cobalt hydrocarbonyl to produce a mixture of 1- and 2-pentylcobalt tetracarbonyls was shown to be inhibited by carbon monoxide (46). The inhibition very likely arises because the reactive species is cobalt hydrotricarbonyl rather than the tetracarbonyl. The carbon monoxide, by a mass action effect, reduces the concentration of the reactive species. 

Cobalt hydrocarbonyl is a very reactive compound. It reacts extremely rapidly with triphenylphosphine, probably by a first-order dissociation mechanism, producing cobalt hydrotricarbonyl triphenylphosphine (44). This demonstrates the very ready replacement of one ligand by another. Cobalt hydrocarbonyl also catalyzes the isomerization of olefins. Under conditions of the hydroformylation reaction, olefin isomerization is observed. But there is controversy as to whether or not rearranged aldehydes (aldehydes which cannot be produced by simple addition to the starting olefin) are produced mainly by rearrangement of an intermediate in the reaction (28, 75, 55) or by reaction of isomerized olefins (55). 

Despite very extensive studies on this reaction, there is still considerable uncertainty about its mechanism. The reaction occurs at about the same rate in a wide variety of organic solvents, including benzene, heptane, and alcohol, suggesting that polar intermediates are not involved (Wender et al., 41). Reaction of the olefin with preformed cobalt hydrocarbonyl also gives the aldehyde product (Wender et al., 4 ). This, together with the observation that cobalt hydrocarbonyl is formed under hydroformylation conditions in the absence of olefin, but cannot be detected in the presence... 

The noncatalytic reaction of cobalt hydrocarbonyl with olefins to produce aldehydes... 

When a large excess of olefin was used, the cobalt hydrocarbonyl was completely used up in Eq. (2), and Eq. (3) did not occur. In this case the products have been recovered as the triphenylphosphine derivatives, or as the esters by reaction of the acylcobalt carbonyls with iodine and an alcohol. 

Prior to Takegami s studies, the effect of isomerization of acylcobalt carbonyls on the products of the reaction between cobalt hydrocarbonyl and olefins had received little attention. Terminal olefins had been found to give a mixture of linear and branched products at low temperatures under carbon monoxide, and this was taken as reflecting the mode of addition of cobalt hydrocarbonyl (62, 73, 147). In view of the slow rate of isomerization of acylcobalt carbonyls this seems justified. However, it is worth noting that branched products predominated in the reaction of 1-pentene with hydrocarbonyl under nitrogen even when the olefin had isomerized only to the extent of 50% (73). Both isobutylene and alkyl acrylates had been found to produce branched products. It was suggested that isobutylene, with an... 

Takegami et al. (147) reexamined the reaction of olefins with cobalt hydrocarbonyl to determine the effect of reaction variables and the possibility of isomerization on the structure of the acylcobalt carbonyls formed. Products were recovered as their ethyl esters as described previously. Additionally, the uptake of carbon monoxide was measured. This is important since the presence of an acylcobalt tricarbonyl can be inferred when the amount of ester produced exceeds the amount of carbon monoxide absorbed. 

In view of the fact that no free hydrocarbonyl is normally detected in the presence of olefin under Oxo conditions (92, 107), Eq. (22) seems more likely than Eq. (21). 

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)). 

The present authors feel this point needs further investigation in view of the results of Takegami et al. They found that the isomerization of the acylcobalt tetracarbonyl was very solvent-dependent, and it could well be that conditions in the hydroformylation of olefins and orthoformates were sufficiently different to cause faster isomerization in the former case. Thus, for example, the presence of olefins in the former case may contribute to a faster isomerization, or perhaps orthoformates, like tetrahydrofuran, inhibit the isomerization. A further factor to be considered is the presence of cobalt hydrocarbonyl, which must be present in larger amount in the case of olefin hydroformylation. Takegami et al. (143) have shown that cobalt hydrocarbonyl strongly promotes the isomerization of phenylacetylcobalt car-... 

Some light has been thrown on this unusual reaction by a study of the reaction of cobalt hydrocarbonyl with olefins under nitrogen (14). It has also be discussed recently by Heck (59). 

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. 

As with the hydroformylation of olefins, aldehydes are expected by a reduction of acylcobalt carbonyls by cobalt hydrocarbonyl. They are formed in small amounts for a number of epoxides (145). 

In view of the many differences noted above between the hydroformylation of olefins and epoxides, it is not surprising to find that changes in structure result in a different order of reactivity in each case. Thus for epoxides the reactivity to cobalt hydrocarbonyl is cyclohexene oxide > propylene oxide, whereas with olefins the order is terminal olefins > internal olefins > cyclic olefins (145). 

Originally, Piacenti et al. explained the formation of isomeric products in terms of an equilibrium of alkylcobalt carbonyls with olefin-hydrocarbonyl complexes as in the Oxo reaction. More recently, however, they have noted that the conditions under which n-propyl orthoformate gave no isomeric products (below 150° C, carbon monoxide pressure 10 atm) are conditions under which isomerization occurs readily in the hydroformylation of olefins (115). Since alkylcobalt carbonyls were formed in both reactions they dismissed the possibility that this isomerization was due to alkyl- or acylcobalt carbonyls. The fact that Takegami et al. have found that branched-chain acylcobalt tetracarbonyls isomerize more readily than straight-chain acylcobalt tetracarbonyls would seem to fit in quite well with the results of Piacenti et al., however, and suggests that the two findings may not be so irreconcilable as might at first appear (see Section II, B,2). 

In the absence of olefin, cobalt hydrocarbonyl was identified and demonstrated to react further with silicon hydride as in Eq. (73). 

It has been observed that rapid isomerization accompanies the cobalt carbonyl-catalyzed hydrosilation of olefins (18). The reaction of equimolar amounts of a trisubstituted silane and dicobalt octacarbonyl has been shown to result in the formation of cobalt hydrocarbonyl (cf. Section IV). A very effective isomerization catalyst may be prepared by treatment of a solution of Co2(CO)8 in olefin ( 0.01 M) with a silicon hydride in sufficient quantity to slightly exceed the cobalt carbonyl concentration. 

An application to a considerably more complex reaction is shown in the next example, that of hydroformylation of olefins with a cobalt hydrocarbonyl catalyst. 

Example 6.5. Olefin hydroformylation with phosphine-substituted cobalt hydrocarbonyl catalyst [30], The pathway 6.9 of olefin hydroformylation with the "oxo" catalyst, HCo(CO)4, has been shown in Example 6.2 in Section 6.3. For phosphine-substituted catalysts, HCo(CO)3Ph (Ph = organic phosphine), the pathway olefin — aldehyde is essentially the same. However, these catalysts also promote hydrogenation of aldehyde to alcohol (Examples 7.3 and 7.4) and of olefin to paraffin (Example 7.5). Moreover, straight-chain primary aldehydes under the conditions of the reaction undergo to some extent condensation to aldol, which is subsequently dehydrated and hydrogenated to yield an alcohol of twice the carbon number (e.g., 2-ethyl hexanol from n-butanal see Section 11.2). The entire reaction system is... 

Example 7.5. Olefin hydrvformylation with paraffin by-product formation [7,9]. Hydroformylation of olefins to aldehydes, catalyzed by a phosphine-substituted cobalt hydrocarbonyl, HCo(CO)3Ph (Ph = tertiary organic phosphine), has been used for illustration in examples 5.2 and 5.3 in Sections 5.2 and 5.3. The catalyst also promotes hydrogenation, so aldehyde produced from olefin is converted to alcohol, and paraffin is formed from olefin as by-product ... 

Example 7.6. Olefin hydroformylation with phosphine-substituted cobalt hydrocarbonyl catalyst [7], The overall reaction system of olefin hydroformylation with a phosphine-substituted cobalt hydrocarbonyl catalyst to produce alcohol, paraffin, and a heavy alcohol has been shown in Example 6.5 (Section 6.5) ... 

Cobalt hydrocarbonyl-catalyzed olefin hydroformylation with network 6.9 may serve as an example. Cobalt, with atomic number 27, contributes nine valence electrons to its complexes (the other eighteen occupy the inner 1-5, 2-s, 2-p, 3-5, and 3-p orbitals) H, the alkyl group, and the acyl group contribute one each, CO contributes two (of its fourteen electrons, four are shared by C and O in the double bond, an additional four each complete the inner octets of C and O), and an olefin ligand contributes the two Tr-electrons of its double bond. The contributions and totals for some key participants are ... 

Example 8.3. Phosphine-substituted cobalt hydrocarbonyls as hydroformylation catalysts. Extensively studied catalyst systems with complex equilibria include phosphine-substituted hydrocarbonyls of cobalt, HCo(CO)3Ph, where Ph stands for a tertiary organic phosphine. They are modifications of the original oxo catalyst, HCo(CO)4. Like the latter, they catalyze the oxo or hydroformylation reaction of olefins to aldehydes one carbon number higher ... 

Example 8.11. Hydrcformylation with phosphine-substituted cobalt hydrocarbonyl catalyst. The phosphine-substituted cobalt hydrocarbonyl catalyst used for hydro-formylation of olefins has been described in Section 8.2 (see network 8.13). The principal reaction... 

Examples include acetal hydrolysis, base-catalyzed aldol condensation, olefin hydroformylation catalyzed by phosphine-substituted cobalt hydrocarbonyls, phosphate transfer in biological systems, enzymatic transamination, adiponitrile synthesis via hydrocyanation, olefin hydrogenation with Wilkinson s catalyst, and osmium tetroxide-catalyzed asymmetric dihydroxylation of olefins. 

Figure 12.4. Instantaneous isothermal heat release Q as function of olefin conversion for hydroformylation of long-chain olefins with cobalt phosphino-hydrocarbonyl catalysts (schematic).

Example 12.2. Potential mass transfer-induced instability in olefin hydroformylation [14]. The rate of olefin hydroformylation with cobalt hydrocarbonyl catalysts in a liquid phase obeys in good approximation the Martin equation... 

Many other addition reactions of olefins, dienes, and acetylenes are known, which are catalyzed by metal carbonyls including Ni(CO)4, Fe(CO)5, and Co2(CO)8 and by carbonyl derivatives such as hydrocarbonyls or phosphine-substituted carbonyls. Among these are the hydro-carboxylation, hydroesterification, and hydrocyanation of olefins the synthesis of hydroquiniones from acetylenes, carbon monoxide, and water ... 

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