Olefin complexes hydroformylation

By analogy with hydroformylation, dicobalt octacarbonyl has been examined as a hydrosilylation catalyst. Various silanes and a-olefins react, often exothermically. Thermal deactivation occurs above 60° C hence, large exotherms and high temperatures must be avoided (56, 57,130). Isomerization is more pronounced than for the bridged olefin complexes of Pt(II) and Rh(I) (see below) it even occurs with trialkoxysilanes (57). Though isomerization is faster than hydrosilylation, little variation in the relative rates of these two processes with the nature of the silane is observed this is in marked contrast to the bridged systems (55). 

Abstract Aldehydes obtained from olefins under hydroformylation conditions can be converted to more complex reaction products in one-pot reaction sequences. These involve heterofunctionalization of aldehydes to form acetals, aminals, imines and enamines, including reduction products of the latter in an overall hydroaminomethylation. Furthermore, numerous conversions of oxo aldehydes with additional C.C-bond formation are conceivable such as aldol reactions, allylations, carbonyl olefinations, ene reactions and electrophilic aromatic substitutions, including Fischer indole syntheses. 

Figure 1 outlines the key intermediates of a catalytic cycle where the rate-determining step is the formation of an n-alkyl derivative of the trans-bisphosphine via a coordinated olefin complex. This presumed catalytic cycle appears to satisfy proposals by Cavalieri d Oro et al. (9), C. V. Pittman et al. (10), and J. Hjortkjaer (II). Although no single mechanism of hydroformylation was established, the cycle is shown here to illustrate the key nature of the equilibrium between the trisphosphine (D) and the trans-bisphosphine (E). 

The fact that a model for the transition state controlling asymmetric induction based on steric interactions allows us to correctly predict the type of prevailing regio- and stereoisomer for about 85% of the asymmetric hydrocarbonylation experiments (including hydroformylation and hydrocarbalkoxylation) is an indication that asymmetric induction in these catalytic reactions is based mainly on steric interactions. The data obtained so far do not allow us to establish whether the more stable or the less stable 7r-olefin complex intermediate is the one that reacts preferentially. However, the regularities that we observed indicate that the kinetic features are the same, at least in most of the experiments. 

Using the same model and considering the results of the investigation of square planar platinum(II)-chiral olefin complexes 61-63> it is possible to correlate enantio-face discriminating hydroformylation with enantiomer discriminating hydroformy-lation. 

As shown in the asymmetric hydroformylation of 1- and 2-butene with Rh/(--)-DIOP or Pt/(—)-DIOP catalytic systems, it seems likely that asymmetric induction occurs mainly in the step in which the n-olefin complexes, which are assumed to be formed in the first reaction step, are transformed into the corresponding metal-alkyl intermediate 15). 

In the hydroformylation of 1-hexene with the same catalyst, at high olefin concentrations (>0.5 mol/L) the reaction rates decrease with increasing substrate concentration [112]. In this concentration range the reaction rate is negative order in olefin concentration. The maximum of the reaction rates varies with the polarity of the solvent [113]. This inhibiting effect was explained by formation of an olefin complex of an alkylrhodium species, which is no longer part of the... 

While the intimate mechanism of the hydroformylation reaction awaits further study, the course of the reaction and the nature of the intermediates seem fairly well defined. The concept that a carbonyl-olefin complex such as II is the only immediate source of hydrogen and carbon monoxide and that the transfer of hydrogen and carbon monoxide to the olefin takes place within this complex is an aid in our understanding of the nature and the role of intermediates in catalytic reactions. 

Rhodium complex Hydroformylation Olefin + products Sodium n-dodecyl 79... 

Rhodium complex Hydroformylation Olefin+ Sodium n-dodecyl sulfate 7-120 > 79... 

Another catalytic cycle studied by Matsubara, Morokuma, and coworkers [77] is the hydroformylation of olefin by an Rh(I) complex. Hydroformylation of olefin by the rhodium complex [78-80] is one of the most well known homogeneous catalytic reactions. Despite extensive studies made for this industrially worthwhile reaction [81, 82], the mechanism is still a point of issue. The active catalyst is considered to be RhH(CO)(PPh3)2, 47, as presented in Fig. 25. The most probable reaction cycle undergoes CO addition and phosphine dissociation to generate an active intermediate 41. The intramolecular ethylene insertion, CO insertion, H2 oxidative addition, and aldehyde reductive elimination are followed as shown with the surrounding dashed line. Authors have optimized the structures of nearly all the relevant transition states as well as the intermediates to determine the full potential-... 

With added CO, but not in its absence, ethylene reacts rapidly with HRh(CO)L3 solutions to give the acyl complex EtCORh(CO)2iL2- With 1 atm of H2 and CO (in a 2 1 ratio) propionaldehyde forms with a half-life of 5 minutes. Using a 1 2 mixture of H2 and CO instead of 2 1 increases the half-life to an hour, suggesting that CO dissociation from the 18-electron acyl complex is necessary before oxidative addition of H2. Isomerization and hydrogenation are much slower under hydroformylation conditions (with H2 and CO) than under H2 alone. These reactions are typically only 1-2% of the hydroformylation rate. The reason must be high rates of capture of 16-electron alkyl rhodium complexes by CO compared to rates of H2 capture or jS -hydride abstraction to form isomerized hydrido-olefin complexes. 

Heck has formulated a mechanism which accounts for hydroformylation of olefins catalyzed by cobalt carbonyl (68). A modification of this mechanism is presented in Fig. 5. Cobalt octacarbonyl reacts with hydrogen to form the tetracarbonyl hydride. It is proposed that this coordinatively saturated complex loses a CO group to form the four-coordinate hydride (LX). Coordination of an olefin yields the olefin complex (LXI). Migration of hydride yields an unsaturated alkyl complex (LXII). Further insertion of a CO group (undoubtedly by a migration mechanism) affords the four-coordinate acyl cobalt(I) complex (LXIII). Oxidative addition of hydrogen affords the hypothetical dihydride (LXIV), which eliminates the product aldehyde and regenerates the cobalt(I) hydride catalyst (LX). This latter... 

In 2012, the scope of substrates was extended to a series of functionalized alkenes [20]. Allyl alcohol produced only 31% of the desired alcohol, but a significant reduction of the olefin was complained about. The formation of y-isobutyrolactone was also observed. In contrast, longer alkenyl alcohols produced up to 95% (e.g., 1,6-hexanediol) of the desired diols. Protection of the alcoholic group (THP, Ac, Bn) had only a sUght effect. The contribution of the individual metal complexes to the single steps (olefin isomerization, hydroformylation, and hydrogenation) was clarified in a kinetic study. 

A mechanism was suggested on the basis of deuteration labeling studies and by the isolation of some intermediates (Scheme 8.17) [4]. In the first stage, the catalyst 1 is loaded with the substrate aldehyde. Under the effect of benzoic acid, the hydrido-Rh-acyl complex 2 is formed. After decarbonylation of the acyl unit, the corresponding Rh-alkyl complex 4 is obtained, which is immediately converted into the jc-olefin complex 5. Exchange of the olefin by the formyl acceptor olefin (here NBD) and subsequent hydroformylation of the latter result in the net transfer of the formyl group from one aldehyde to the other. 

Olefin-CO coploymers Olefin p-complexes Olefin Fibers Olefin hydroformylation Olefin hydrogenation Olefimc alcohols Olefin isomerization Olefin metathesis Olefin oligomers Olefin oxides... 

Often the aldehyde is hydrogenated to the corresponding alcohol. In general, addition of carbon monoxide to a substrate is referred to as carbonylation, but when the substrate is an olefin it is also known as hydroformylation. The eady work on the 0x0 synthesis was done with cobalt hydrocarbonyl complexes, but in 1976 a low pressure rhodium-cataly2ed process was commerciali2ed that gave greater selectivity to linear aldehydes and fewer coproducts. 

The switch from the conventional cobalt complex catalyst to a new rhodium-based catalyst represents a technical advance for producing aldehydes by olefin hydroformylation with CO, ie, by the oxo process (qv) (82). A 200 t/yr CSTR pilot plant provided scale-up data for the first industrial,... 

A new homogeneous process for hydroformylation of olefins using a water-soluble catalyst has been developed (40). The catalyst is based on a rhodium complex and utilizes a water-soluble phosphine such as tri(M-sulfophenyl)phosphine. The use of an aqueous phase simplifies the separation of the catalyst and products (see Oxo process). 

Olefin Hydroformylation (The Oxo Process). One of the most important iadustrial applications of transition-metal complex catalysis is the hydroformylation of olefins (23), ihusttated for propjdene ... 

Polymer-supported catalysts incorporating organometaUic complexes also behave in much the same way as their soluble analogues (28). Extensive research has been done in attempts to develop supported rhodium complex catalysts for olefin hydroformylation and methanol carbonylation, but the effort has not been commercially successful. The difficulty is that the polymer-supported catalysts are not sufftciendy stable the valuable metal is continuously leached into the product stream (28). Consequendy, the soHd catalysts fail to eliminate the problems of corrosion and catalyst recovery and recycle that are characteristic of solution catalysis. 

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. 

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