Hydroformylation carbonyl insertion

These sites must be considered to have different catalytic properties. The sites on top (Co atoms of low coordination) would be similar to that of the central atom of cobalt carbonyl complexes, and reactions on these should be similar to those in hydroformylation. Specifically, insertion reactions between n- and cr-ligands (CO... 

Interception of the reaction sequence at the alkylcobalt carbonyl stage before carbonyl insertion, and hydrogenation of this intermediate, produces an alkane. This undesired side reaction is only minor (1-3%) in cobalt-catalyzed hydroformylation of a nonfunctional olefin, but may become predominant with phenyl- or acyl-substituted olefins. Ethylbenzene has been obtained in >50% yield from styrene (37), and even more alkane was obtained from a-methylstyrene (35). 

Monsanto acetic acid synthesis 4), and the hydroformylation or 0X0 reaction (5). A key mechanistic step in catalytic carbonylation reactions is the migration of an alkyl group onto an adjacent carbonyl ligand. This reaction involves the formation of a new carbon-carbon bond and has been termed a carbonyl insertion reaction since a CO ligand has been formally inserted into the transition metal-carbon (r-bond. Because of the industrial and commercial importance of these catalytic reactions, the search for stoichiometric systems in which this step can be observed directly has been, and still is, one of great endeavor. 

The insertion of CO into a C(sp )-Pd or C(sp )-Pd species is a common procedure and it is applicable to a wide range of reactions, such as hydroformylation, carbonylation, hydroesterification and so on, thus being an ideal terminating transformation within a domino process starting, for example, with a Mizoroki-Heck reaction. 

The key carbonyl insertion reaction which is involved in both hydroformylation and the Fischer.-Tropsch reaction can be reversible. This reaction is of occasional... 

CO insertion (as inferred from the nature of products), but in which the actual insertion or decarbonylation step has received at most peripheral attention. This particularly applies to industrial carbonylation processes such as hydroformylation. The interested reader is referred to several excellent articles on these subjects (30, 32, 62, 117, 198a, 203a, 228). 

The carbonyl [CpFe(CO)2]2 has been successfully employed as a catalyst for hydroformylation of propylene (229) and for the reaction in Eq. (55) (221). Insertion of CO into Fe—C bonds is thought to occur therein. 

Tandem procedures under hydroformylation conditions cannot only make use of the intrinsic reactivity of the aldehyde carbonyl group and its acidic a-position but they also include conversions of the metal alkyl and metal acyl systems which are intermediates in the catalytic cycle of hydroformylation. Metal alkyls can undergo -elimination leading to olefin isomerization, or couplings, respectively, insertion of unsaturated units enlarging the carbon skeleton. Similarly, metal acyls can be trapped by addition of nucleophiles or undergo insertion of unsaturated units to form synthetically useful ketones (Scheme 1). 

The insertion of CO is in many instances thermodynamically unfavourable the thermodynamically most favourable product in hydroformylation and carbonylation reactions of the present type is always the formation of low or high-molecular weight alkanes or alkenes, if chain termination occurs via (3-hydride elimination). The decomposition of 3-pentanone into butane and carbon monoxide shows the thermodynamic data for this reaction under standard conditions. Higher pressures of CO will push the equilibrium somewhat to the left. 

Ethylene hydroformylation was treated as a separate case, as difSculties arise from dramatic changes in the IR spectrum of dissolved ethylene as a function of its partial pressure. This was overcome using the method of band-target entropy minimisation (BTEM, see Chapter 4) to recover the pure component spectra of all observable species and their concentrations [72]. As well as the conventional acyl tetra-carbonyl, [Rh(C(0)Et)(C0)4], evidence was obtained for [Rh(C(0)Et)(C0)3(C2H4)], containing coordinated ethylene. The presence of this species indicates that ethylene can compete with H2 for the unsaturated [Rh(C(0)Et)(C0)3]. The ketone and polyketone side products of Rh-catalysed ethylene hydroformylation arise from insertion of coordinated ethylene into the Rh-acyl bond in [Rh(C(0)Et)(C0)3(C2H4) ... 

The formation of formate esters in the hydroformylation reaction (90, 64) may be explained by a CO-alkoxide insertion reaction as well as by the CO-hydride insertion mechanism mentioned above. Aldehydes formed in the hydroformylation reaction can be reduced by cobalt hydrocarbonyl (27) presumably by way of an addition of the hydride to the carbonyl group (90, 2). If the intermediate in the reduction is an alkoxycobalt carbonyl, carbon monoxide insertion followed by hydrogenation would give formate esters (90, 64). 

If the formation of formate esters under hydroformylation conditions involves the carbonylation of an alkoxycobalt carbonyl as suggested previously (90), this would be evidence that cobalt hydrocarbonyl adds the reverse way to acyl groups. Since the formation of formate esters can be explained as well by a CO insertion into a cobalt-hydrogen group followed by alcoholysis, however, the data would be explained best if a cobalt-carbon bond was formed in the hydride reduction of acyl compounds. 

Another possible reason that ethylene glycol is not produced by this system could be that the hydroxymethyl complex of (51) and (52) may undergo preferential reductive elimination to methanol, (52), rather than CO insertion, (51). However, CO insertion appears to take place in the formation of methyl formate, (53), where a similar insertion-reductive elimination branch appears to be involved. Insertion of CO should be much more favorable for the hydroxymethyl complex than for the methoxy complex (67, 83). Further, ruthenium carbonyl complexes are known to hydro-formylate olefins under conditions similar to those used in these CO hydrogenation reactions (183, 184). Based on the studies of equilibrium (46) previously described, a mononuclear catalyst and ruthenium hydride alkyl intermediate analogous to the hydroxymethyl complex of (51) seem probable. In such reactions, hydroformylation is achieved by CO insertion, and olefin hydrogenation is the result of competitive reductive elimination. The results reported for these reactions show that olefin hydroformylation predominates over hydrogenation, indicating that the CO insertion process of (51) should be quite competitive with the reductive elimination reaction of (52). 

Of the isomeric aldehydes indicated in Eq. (7.1), the linear aldehyde corresponding to anti-Markovnikov addition is always the main product. The isomeric branched aldehyde may arise from an alternative alkene insertion step to produce the [RCH(Me)Co(CO)3] or [RCH(Me)Rh(CO)(PPh3)2] complexes, which are isomeric to 2 and 8, respectively. Alternatively, hydroformylation of isomerized internal alkenes also give branched aldehydes. The ratio of the linear and branched aldehydes, called linearity, may be affected by reaction conditions, and it strongly depends on the catalyst used. Unmodified cobalt and rhodium carbonyls yield about 3-5 1 mixtures of the normal and iso products. 

The metal hydride mechanism was first described for the cobalt-carbonyl-catalyzed ester formation by analogy with hydroformylation.152 It was later adapted to carboxylation processes catalyzed by palladium136 153 154 and platinum complexes.137 As in the hydroformylation mechanism, the olefin inserts itself into the... 

Another important reaction typically proceeding in transition metal complexes is the insertion reaction. Carbon monoxide readily undergoes this process. Therefore, the insertion reaction is extremely important in organoiron chemistry for carbonylation of alkyl groups to aldehydes, ketones (compare Scheme 1.2) or carboxylic acid derivatives. Industrially important catalytic processes based on insertion reactions are hydroformylation and alkene polymerization. 

Hydrogenolysis of Co2(CO)8 generates hydrocobalt carbonyl 35 as a catalyst precursor. The hydroformylation is explained by the insertion of propylene to hydrocobalt carbonyl 36 to give propylcobalt 37. Then CO insertion generates the... 

The most intensely studied insertion reactions are those of CO into metal—carbon bonds to form metal acyls. These reactions are fundamental to industrially important catalytic reactions such as carbonylation and hydroformylations (Sections 22-5 and 22-6). 

Extensive mechanistic studies have been performed on reactions catalyzed by rhodium and platinum complexes containing enantiopure C2-symmetric diphosphine ligands.As discussed above, (1) the formation of the Tr-olefin-Rh(H) complex 19, (2) stereospecific cis addition of the hydridorhodium to the coordinated olefin to form the alkyl-Rh complex 20 (and then 2, and (3) the migratory insertion of a carbonyl ligand giving the acyl-Rh complex 17 with retention of configuration, have been established in the hydroformylation of 1-alkenes or substituted ethenes. Thus, it is reasonable to assume that the enantioselectivity of the reaction giving a branched aldehyde is determined at the diastereomeric (1) TT-olefin-Rh complex 19 formation step, (2) alkyl-Rh complex 20 formation step, or (3) acyl-Rh complex 17 formation step. 

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