Vinyl hydroformylation

Isobutyraldehyde is commonly available as a by-product of propylene/Oxo hydroformylation. Methyl isoamyl ketone is used as a solvent for ceUulose esters, acryHcs, and vinyl polymers. It is available in the United States from Eastman (Kingsport, Tennessee) (47) and Union Carbide (South Charleston, West Virginia) and was priced at 1.42/kg in October 1994. 

Conceptually at least, these compounds can be obtained via initial enantioselective hydroformylation of the appropriate vinyl aromatic to branched chiral aldehyde and subsequent oxidation. 

Olefin isomerization can be catalyzed by a number of catalysts such as molybdenum hexacarbonyl [13939-06-5] Mo(CO)g. This compound has also been found to catalyze the photopolymerization of vinyl monomers, the cyclization of olefins, the epoxidation of alkenes and peroxo species, the conversion of isocyanates to carbodiimides, etc. Rhodium carbonylhydrotris(triphenylphosphine) [17185-29-4] RhH(CO)(P(CgH )2)3, is a multifunctional catalyst which accelerates the isomerization and hydroformylation of alkenes. 

Hydroformylation of vinyl acetate to give mainly the branched product in >90% ee has been achieved using a rhodium catalyst containing binaphthol and phosphine ligands anchored to polystyrene. 

Betzemeier et al. (1998) have used f-BuOOH, in the presence of a Pd(II) catalyst bearing perfluorinated ligands using a biphasic system of benzene and bromo perfluoro octane to convert a variety of olefins, such as styrene, p-substituted styrenes, vinyl naphthalene, 1-decene etc. to the corresponding ketone via a Wacker type process. Xia and Fell (1997) have used the Li salt of triphenylphosphine monosulphonic acid, which can be solubilized with methanol. A hydroformylation reaction is conducted and catalyst recovery is facilitated by removal of methanol when filtration or extraction with water can be practised. The aqueous solution can be evaporated and the solid salt can be dissolved in methanol and recycled. 

Related systems are the bis-diazaphospholane ligands of which ESPHOS has proved optimal. Best results were obtained upon hydroformylation of vinyl acetate with ee values up to 89% for the branched lactalde-hyde acetate (Scheme 23) [72], Even more efficient variations are bis-3,4-diazaphospholane ligands, which furnished up to 96% ee upon hydroformylation of vinyl acetate [73]. 

The cA-PtCl2(diphosphine)/SnCl2 constitutes the system mostly used in catalyzed hydroformylation of alkenes and many diphosphines have been tested. In the 1980s, Stille and co-workers reported on the preparation of platinum complexes with chiral diphosphines related to BPPM (82) and (83) and their activity in asymmetric hydroformylation of a variety of prochiral alkenes.312-314 Although the branched/normal ratios were low (0.5), ees in the range 70-80% were achieved in the hydroformylation of styrene and related substrates. When the hydroformylation of styrene, 2-ethenyl-6-methoxynaphthalene, and vinyl acetate with [(-)-BPPM]PtCl2-SnCl2 were carried out in the presence of triethyl orthoformate, enantiomerically pure acetals were obtained. 

Most of the reports on Rh-catalyzed asymmetric hydroformylation are concerned with asymmetric hydroformylation of vinyl aromatics, which are model substrates of interest to the pharmaceutical industry. In 1993 and 1995, reports were published describing the state of the art in hydroformylation with both rhodium and platinum systems.80,81 310 Two reports appeared in 1999 and 2000 on carbonylation and rhodium asymmetric hydroformylation respectively.311,345... 

Rh(acac)(CO)2] in combination with ESPHOS (76a) was applied in the asymmetric hydroformylation of vinyl acetate with excellent results. ESPHOS was effective in styrene hydroformylation, but the product is essentially racemic.270... 

The first reports on asymmetric hydroformylation using diphosphite ligands revealed no asymmetric induction. In 1992, Takaya et al. published the results of the asymmetric hydroformylation of vinyl acetate (ee = 50%) with chiral diphosphites.358... 

Rhodium precipitation in solubilized rhodium-phosphite complex catalyzed liquid recycle hydroformylation may be minimized or prevented by carrying out product recovery in the presence of an organic polymer containing polar functional groups such as amides, ketones, carbamates, ureas and carbonates.[20] Patent examples include the use of polyvinylpyrrolidone and vinylpyrrolidone-vinyl acetate copolymer with diorganophosphite-modified rhodium catalysts. 

Arya et al. used solid phase synthesis to prepare immobilised dendritic catalysts with the rhodium centre in a shielded environment to mimic nature s approach of protecting active sites in a macromolecular environment (e.g. catalytic sites inside enzymes) [51], Two generations PS immobilised rhodium-complexed dendrimers, 6 and the more shielded 7, were synthesised.The PS resin immobilised rhodium-complexed dendrimers were used in the hydroformylation of styrene, p-methoxystyrene, vinyl acetate and vinyl benzoate using a total pressure of 70 bar 1 1 CO/H2 at 45 °C in CH2C12. 

Another route to the diol monomer is provided by hydroformylation of allyl alcohol or allyl acetate. Allyl acetate can be produced easily by the palladium-catalyzed oxidation of propylene in the presence of acetic acid in a process similar to commercial vinyl acetate production. Both cobalt-and rhodium-catalyzed hydroformylations have received much attention in recent patent literature (83-86). Hydroformylation with cobalt carbonyl at 140°C and 180-200 atm H2/CO (83) gave a mixture of three aldehydes in 85-99% total yield. 

Early studies of the cobalt hydroformylation (4) included vinyl acetate as the olefinic reactant. A mixture of a- and /3-formyl esters was reported. 

Falbe and Korte (90) studied the cobalt hydroformylation of dihydro-pyran and its derivatives. The reactions were conducted at temperatures above 180°C, with pressures of 300 atm of 1/1 H2/CO. Under these conditions, the initially formed aldehydes were hydrogenated to the alcohols in situ. As noted with acyclic vinyl ethers, formyl attachment was predominantly a. 

Rhodium-Catalyzed Asymmetric Hydroformylation of Vinyl Arenes. .. 41... 

Abstract This chapter presents the latest achievements reported in the asymmetric hydroformylation of olefins. It focuses on rhodium systems containing diphosphites and phosphine-phosphite ligands, because of their significance in the subject. Particular attention is paid to the mechanistic aspects and the characterization of intermediates in the hydroformylation of vinyl arenes because these are the most important breakthroughs in the area. The chapter also presents the application of this catalytic reaction to vinyl acetate, dihydrofurans and unsaturated nitriles because of its industrial relevance. 

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