Hydroformylation using cobalt carbonyls

Acetylenes have been found difficult to hydroformylate. Using cobalt carbonyl catalysts only low yields of aldehydes were obtained from 1-pen-tyne [105]. With the catalyst precursor (PhsPjsRhCl in ethanol-benzene, 1-hexyne reacts with 1 4 mixtures of H2 and CO at 110V120 atm. to give about a 15% yield of n-heptaldehyde and 2-methylhexaldehyde in equal amounts [48]. 

The first stage of the process is a hydroformylation (oxo) reaction from which the main product is n-butyraldehyde. The feeds to this reactor are synthesis gas (CO/H2 mixture) and propylene in the molar ratio 2 1, and the recycled products of isobutyraldehyde cracking. The reactor operates at 130°C and 350 bar, using cobalt carbonyl as catalyst in solution. The main reaction products are n- and isobutyraldehyde in the ratio of 4 1, the former being the required product for subsequent conversion to 2-ethylhexanol. In addition, 3 per cent of the propylene feed is converted to propane whilst some does not react. 

An early attempt to hydroformylate butenediol using a cobalt carbonyl catalyst gave tetrahydro-2-furanmethanol (95), presumably by aHybc rearrangement to 3-butene-l,2-diol before hydroformylation. Later, hydroformylation of butenediol diacetate with a rhodium complex as catalyst gave the acetate of 3-formyl-3-buten-l-ol (96). Hydrogenation in such a system gave 2-methyl-1,4-butanediol (97). 

C-19 dicarboxyhc acid can be made from oleic acid or derivatives and carbon monoxide by hydroformylation, hydrocarboxylation, or carbonylation. In hydroformylation, ie, the Oxo reaction or Roelen reaction, the catalyst is usually cobalt carbonyl or a rhodium complex (see Oxo process). When using a cobalt catalyst a mixture of isomeric C-19 compounds results due to isomerization of the double bond prior to carbon monoxide addition (80). 

The industrially used homogeneous catalysts for the hydroformylation of higher molecular olefins into aldehydes, which are hydrogenated to the corresponding surfactant alcohols, are cobalt carbonyl [47] or cobalt carbonylItert-phosphine complexes [48]. 

If cobalt carbonylpyridine catalyst systems are used, the formation of unbranched carboxylic acids is strongly favored not only by reaction of a-olefins but also by reaction of olefins with internal double bonds ( contrathermo-dynamic double-bond isomerization) [59]. The cobalt carbonylpyridine catalyst of the hydrocarboxylation reaction resembles the cobalt carbonyl-terf-phos-phine catalysts of the hydroformylation reaction. The reactivity of the cobalt-pyridine system in the hydrocarboxylation reaction is remarkable higher than the cobalt-phosphine system in the hydroformylation reaction, especially in the case of olefins with internal double bonds. This reaction had not found an industrial application until now. 

Hydroformylation is an important industrial process carried out using rhodium phosphine or cobalt carbonyl catalysts. The major industrial process using the rhodium catalyst is hydroformylation of propene with synthesis gas (potentially obtainable from a renewable resource, see Chapter 6). The product, butyraldehyde, is formed as a mixture of n- and iso- isomers the n-isomer is the most desired product, being used for conversion to butanol via hydrogenation) and 2-ethylhexanol via aldol condensation and hydrogenation). Butanol is a valuable solvent in many surface coating formulations whilst 2-ethylhexanol is widely used in the production of phthalate plasticizers. 

Cobalt carbonyls are the oldest catalysts for hydroformylation and they have been used in industry for many years. They are used either as unmodified carbonyls, or modified with alkylphosphines (Shell process). For propene hydroformylation, they have been replaced by rhodium (Union Carbide, Mitsubishi, Ruhrchemie-Rhone Poulenc). For higher alkenes, cobalt is still the catalyst of choice. Internal alkenes can be used as the substrate as cobalt has a propensity for causing isomerization under a pressure of CO and high preference for the formation of linear aldehydes. Recently a new process was introduced for the hydroformylation of ethene oxide using a cobalt catalyst modified with a diphosphine. In the following we will focus on relevant complexes that have been identified and recently reported reactions of interest. 

Relatively few hydroformylations using supported cobalt complexes have been reported. Moffat (78, 79) showed that poly-2-vinylpyridine reversibly reacted with both Co2(CO) and HCo(CO)4, the cobalt carbonyl being displaced by excess carbon monoxide. This enabled the polymer to pick up the cobalt carbonyl at the end of the reaction and, thus, allowed it to be separated from the products by filtration. The polymer acted as a catalyst reservoir by rapidly releasing the cobalt carbonyl into solution in the presence of further carbon monoxide, so that the actual catalysis was a homogeneous process. More recently, cobalt carbonyl has been irreversibly bound to a polystyrene resin... 

The use of cobalt carbonyls, modified cobalt catalysts, and ligand-modified rhodium complexes, the three most important types of catalysts in hydroformylation,... 

T,he hydroformylation reaction or oxo synthesis has been used on an industrial scale for 30 years, and during this time it has developed into one of the most important homogeneously-catalyzed technical processes (I). A variety of technical processes have been developed to prepare the real catalyst cobalt tetracarbonyl hydride from its inactive precursors, e.g., a cobalt salt or metallic cobalt, to separate the dissolved cobalt carbonyl catalyst from the reaction products (decobaltation) and to recycle it to the oxo reactor. The efficiency of each step is of great economical importance to the total process. Therefore many patents and papers have been published concerning the problem of making the catalyst cycle as simple as possible. Another important problem in the oxo synthesis is the formation of undesired branched isomers. Many efforts have been made to keep the yield of these by-products at a minimum. 

Step 2 Extraction of the Catalyst from the Aqueous Solution. It is not feasible technically to charge the aqueous solution of cobalt carbonyl hydride directly into the hydroformylation reactor because two phases may form, especially with the long chain olefins. The most direct and most efficient way to eliminate water while permitting full use of the carbonyl catalyst is to extract it from the water phase with the olefin intended for hydroformylation. The extraction is carried out between... 

The spacer units in 3.60 are assembled from polyphosphazenes that bear p-bromophc-noxy side groups via a lithiation reaction, and treatment with a diorganochlorophosphine to give 3.62. The chemistry is summarized in reaction sequence (45).107 Polymer 3.62 coordinates to a variety of metallo species,108 including osmium cluster compounds and cobalt carbonyl hydroformylation catalysts. When used as a polymeric hydroformylation catalyst, this latter species proved how stable the polyphosphazene backbone is under the drastic conditions often needed for these types of reactions. The weakest bonds in the molecule proved to be those between the phosphine phosphorus atoms and the aromatic spacer groups. 

The hydroformylation of olefins is one of the largest and most prominent industrial catalytic processes, producing millions of tons of aldehydes annually [102]. Initially, cobalt-carbonyl species were used as catalyst, though rhodium complexes modified by special ligands, usually phosphines, are predominantly used nowadays. Over the last two decades, continued development of new phosphine and phosphite ligands has allowed significant advances in hydroformylation chemistry, especially with respect to catalyst selectivity and stability [103]. 

The synthesis of cobalt carbonyl-boimd silanetriol, Coa(CO)9CSi(OH)a (11) was originally reported by Seyferth et al. (34) by careful hydrolysis of Si—Cl bonds present in Coa(CO)9CSiCla (Scheme 8B). The X-ray crystallographic measurement (35) reveals a cage structure for compound 11. The OH groups present in 11 can be used further for the buildup of a number of heterosiloxanes. The cobalt carbonyl-boimd silanetriol 11 exhibits very high catalytic activity in the hydroformylation of 1-hexene in a biphasic vide infra) system (35). 

Alkenes can be hydroformylated " by treatment with carbon monoxide and hydrogen over a catalyst. The most common catalysts are cobalt carbonyls (see below for a description of the mechanism) and rhodium complexes, " but other transition metal compounds have also been used. Cobalt catalysts are less active than the rhodium type, and catalysts of other metals are generally less active. " Commercially, this is called the 0x0 process, but it can be carried out in the laboratory in an ordinary hydrogenation apparatus. The order of reactivity is straight-chain terminal alkenes > straight-chain internal alkenes > branched-chain alkenes. With terminal alkenes, for example, the aldehyde unit is formed on both the primary and secondary carbon, but proper choice of catalyst and additive leads to selectivity for the secondary product " or primary... 

Hydroformylation reactions are important from the industrial point of view and the two commonly used hydroformylation catalysts are either Rh or Co based. We thought it would be interesting to anchor a SiOs unit on a cobalt cluster via hydrosilylation. This would be a close model to a silica-supported cobalt cluster. Secondly, since the reactions of silanetriols have been demonstrated to afford three-dimensional metallasiloxanes, we anticipated that this silanetriol would react with substrates such as trialkylaluminums, affording cobalt carbonyl cluster anchored aluminosiloxanes. Such compounds would resemble a modified zeolite having on its surface catalytically active cobalt carbonyl moieties and might inspire the preparation of actual zeolite systems with these modifications. 

If cobalt, rhodium and ruthenium complexes are the most frequently used in hydroformylation reactions, most carbonylation reactions employ palladium catalysts. The active water-soluble complex Pd(TPPTS)3 is easily prepared by reducing in situ PdCl2/TPPTS with CO in water at room temperature. The carbonylation of alcohols and olefins (Scheme 1.24) requires the presence... 

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