Hydro formylation, of alkenes

Even if hydrides of transition metals play an important role as intermediates in catalytic processes such as hydrogenation and hydro-formylation of alkenes and the Fischer-Tropsch reaction,71 in order to follow with the bioinorganic subject, we refer to the interconversion process ... 

This sequence of steps is an important part of the mechanism of the hydro-formylation of alkenes (oxo reaction), to be discussed in Section 31-4B, and also is related to the carbonylation reactions of boranes discussed in Section 16-9G. 

The silylcarbonylation of alkenes catalyzed by Co2(CO)s giving homologous silyl enol ethers was reported by Murai and coworkers in 1977 as a silicon version of hydro-formylation of alkenes, and developed as a unique synthetic method302-304. Although... 

Carbonylation (the addition of carbon monoxide to organic molecules) is an important industrial process as carbon monoxide is a convenient one-carbon feedstock and the resulting metal-acyl complexes can be converted into aldehydes, acids, and their derivatives. The 0X0 process is the hydro-formylation of alkenes such as propene and uses two migratory insertions to make higher value aldehydes. Though a mixture is formed this is acceptable from very cheap starting materials. 

NaY zeolite containing [Rhc(CO)i ] has been shown to be a catalyst for the hydro-formylation of alkenes in the liquid phase at 80 C and 80 bar. [38] The catalysts were selective for the formation of butyraldehydes, with a n- to uo-butyraldehyde ratio similar to that shown by mononudear rhodium carbonyls in solutions. [119] The catalyst was also tested for the hydroformylation of nonconjugated dialkenes and produced mainly dialdehydes. [38] The catalyst was recovered after use by decantation and reused with only a small loss in activity. 

Figure 6.1 The fluorous biphase concept illustrated for the hydro formylation of an alkene (substrate) to an...

The selective production of methanol and of ethanol by carbon monoxide hydrogenation involving pyrolysed rhodium carbonyl clusters supported on basic or amphoteric oxides, respectively, has been discussed. The nature of the support clearly plays the major role in influencing the ratio of oxygenated products to hydrocarbon products, whereas the nuclearity and charge of the starting rhodium cluster compound are of minor importance. Ichikawa has now extended this work to a study of (CO 4- Hj) reactions in the presence of alkenes and to reactions over catalysts derived from platinum and iridium clusters. Rhodium, bimetallic Rh-Co, and cobalt carbonyl clusters supported on zinc oxide and other basic oxides are active catalysts for the hydro-formylation of ethene and propene at one atm and 90-180°C. Various rhodium carbonyl cluster precursors have been used catalytic activities at about 160vary in the order Rh4(CO)i2 > Rh6(CO)ig > [Rh7(CO)i6] >... 

Hydroformylation. Using RhjCOAc) in phosphonium tosylates for hydro-formylation of 1-alkenes at 120°, the catalyst recovery is facilitated. Thus, on cooling of the reaction mixture the rhodium acetate is completely retained in the solid phase and the liquid products are obtained by simple decantation. Variation of substituents at the phosphorus atom of ionic solvents [e.g., (PhjPEt) OTs vs. (BUjPEO OTs ] has remarkable effects on the ratio of alkanals and 2-methylalkanals. 

Casey observed a linear/branched ratio of 66 1 using a BISBI-Rh complex to hydroformylate 1-hexene. This is a huge increase over the linear/branched ratio of only 2.6, which Casey observed when a Rh-dppe40 complex is used for hydro-formylation of 1-alkenes.41 The (3n of BISBI is 113-120°, whereas that of dppe is much lower, at 85°. 

Buhling, A. Kamer, P.C.J. Van Leeuwen, P.W.N.M. (1995) Rhodium-catalyzed hydro-formylation of higher alkenes using amphiphilic ligands, J. Mol. Catal. A - Chem., 98, 69-80. 

The desired product in the hydroformylation of allyl alcohol is 4-hydroxybutanal. As with other alkenes, hydro formylation gives both a linear and a branched isomer (Equation 2.1). 

Alkene isomerization has both positive and negative aspects. The positive aspect is where isomerization is needed prior to, for example, hydro formylation to give the desired product. The negative aspect of alkene isomerization is similar to that described in Section 2.6.2.1 on hydrogenation. The byproduct must be separated from both catalyst and product, and recycle opportunities may be limited. Not only is isomerization a direct efficiency loss, but when the isomerised alkene is purged, desired reactants will likely also be lost. 

Hydrocarboxymethylation of Long-Chain Alkenes. An industrial process to carry out hydrocarboxymethylation of olefins to produce methyl esters particularly in the Ci2-Ci4 range for use as a surfactant feedstock was developed by Huels.183 A promoted cobalt catalyst in the form of fatty acid salts (preferably those formed in the reaction) is used. With high promoter catalyst ratio (5 1-15 1) at 180-190°C and pressure of 150-200 atm, the rate of alkene isomerization (double-bond migration) exceeds the rate of hydrocarboxymethylation. As a result, even internal olefins give linear products (the yield of normal products is about 75% at 50-80 % conversion). Secondary transformations of aldehydes (product of olefin hydro-formylation) lead to byproducts (ethers and esters) in small amounts. 

Considering this particular cycle, the question of selectivity on alkene addition is worth considering under normal hydiofonnylation conditions, the isomerization of a coordinated alkene is fast compared to hydro formyl at ion, thus the direction of initial hydride addition is only of marginal importance in determining the rr rsci isomeric ratio. 

Increasing the CO partial pressure decreases the hydro-formylation reaction rate and the amount of alkene isomerization side reactions (see Hydrogenation Isomerization ofAlkenes), while increasing the aldehyde linear to branched product ratio. Pino proposed that the apparent marked difference between HCo(CO)4-catalyzed hydroformylation at low and high CO partial pressures was due to the existence of two active catalyst species, HCo(CO)4 and HCo(CO)3, formed from the CO association/dissociation equilibrium shown in... 

The HCo(CO)4-catalyzed hydrocarboxylation of alkenes has also been known for a long time. The mechanism is analogous to that presented for hydroformyla-tion (Scheme 1), except that H2O is used instead of H2. Hydrocarboxylation is generally slower than hydro-formylation, and it is believed that the concentrations of the intermediate species are quite low relative to those seen for hydroformylation. Pyridine has a rateenhancing effect that is believed to be due to the facile cleavage of the (acyl)Co(CO)4 intermediate. This reaction forms [pyridine-acyl] + [Co(CO)4] , which is more rapidly hydrolyzed by water to form the product carboxylic acid and HCo(CO)4. 

Despite its few binary compounds, the element gives rise to many complexes. Table 1 indicates the diversity of complexes formed. Several low oxidation state complexes of the element are important homogeneous catalysts, particularly in the oligomerization, isomerization. Hydrogenation, Hydro-formylation, Hydroboration, or Hydrosilation of alkenes. lodorhodium complexes catalyze the industrial-scale carbony-lation of methanol to acetic acid. 

An important modern example of homogeneous catalysis is provided by the Monsanto process in which the rhodium compound 1.4 catalyses a reaction, resulting in the addition of carbon monoxide to methanol to form ethanoic acid (acetic acid). Another well-known process is hydro-formylation, in which the reaction of carbon monoxide and hydrogen with an alkene, RCH=CH2, forms an aldehyde, RCH2CH2CHO. Certain cobalt or rhodium compounds are effective catalysts for this reaction. In addition to catalytic applications, non-catalytic stoichiometric reactions of transition elements now play a major role in the production of fine organic chemicals and pharmaceuticals. 

Chelation-assisted additions of formyl C-H bonds to olefins and dienes have been reported by Jun et al. [120]. In the case of the reaction of 8-quinolinecar-boxaldehyde, they proposed that the formation of the stable 5-membered met-allacyclic complex [121] suppressed the undesired decarbonylation reaction (Eq. 53) [120]. The intermolecular hydro acylation of 1-alkene with 2-(diphenyl-phosphino)benzaldehyde by rhodium(I) catalyst has been conducted on the basis of this working hypothesis [122]. 

The following contribution will describe the basics of aqueous two-phase hydro-formylation as they apply to C3 and C4 alkenes. The focus will be on TPPTS (cf. Section 3.2.1) as a ligand and rhodium as the active metal center, e.g., the complex HRh(CO)(TPPTS)3 [1], Emphasis will be put on the commercial applications and the basic description of the processes. 

Scientifically, another major challenge is the development of a biphasic hydro-formylation process for internal alkenes combining isomerization and hydroformy-lation of linear internal alkenes and affording predominantly terminal hydro-formylation products. Such a technology would be of primary interest for the fine chemical and the detergent alcohol markets. 

Ketoximes and oximes of 2-oxo acids are hydrogenated to amines [53], 2-Amino acids can be prepared in high yields by reductive amination of 2-oxo acids in an aqueous NHj solution [Eq. (10)] [54], Aromatic aldehydes were converted with high selectivity to benzylamines by reductive amination with aqueous ammonia catalyzed by a Rh(I)/TPPTS catalyst prepared in situ [55]. In a related, ingenious one-pot process, alkenes were directly converted to primary amines by sequential hydro-formylation, condensation with aqueous ammonia, and hydrogenation of the resulting imines [56],... 

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