Cobalt/phosphine catalyst

Mono- and double carbonylation of phenetyl bromide with cobalt-phosphine catalysts afforded benzylacetic (Baa) and benzylpymvic (Bpa) acids respectively [23] (Scheme 5.5). The highest yield of benzylpymvic acid (75 %) was obtained with [Co2(CO)8], while addition of the water soluble phosphines TPPMS or TPPTS decreased both the yield of carbonylated products and the selectivity to Bpa. 

The Shell process uses a cobalt/phosphine catalyst for the homologation of methanol CH3 - OH 4- CO + 2Hj - CH3CH2OH 4- H20... 

The reaction of norbomadiene with an acetylene may follow different reaction channels, depending on the reaction conditions. Using a cobalt/phosphine catalyst, an acetylene adds to the two unsaturated front carbon atoms of norbomadiene, giving a five-membered cyclopentene ring. Simultaneously, a three-membered cyclopropane ling is formed at the backside of the molecule. The polycyclic skeleton obtained in this homo Diels-Alder reaction is called the deltacyclene skeleton (Scheme 4). 

A particularly useful phosphine ligand for the cobalt carbonyl catalyst is a bicyclic tertiary phosphine available from 1,5-cyclooctadiene, phosphine, and an a-olefin ... 

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. 

The catalysts used in hydroformylation are typically organometallic complexes. Cobalt-based catalysts dominated hydroformylation until 1970s thereafter rhodium-based catalysts were commerciahzed. Synthesized aldehydes are typical intermediates for chemical industry [5]. A typical hydroformylation catalyst is modified with a ligand, e.g., tiiphenylphoshine. In recent years, a lot of effort has been put on the ligand chemistry in order to find new ligands for tailored processes [7-9]. In the present study, phosphine-based rhodium catalysts were used for hydroformylation of 1-butene. Despite intensive research on hydroformylation in the last 50 years, both the reaction mechanisms and kinetics are not in the most cases clear. Both associative and dissociative mechanisms have been proposed [5-6]. The discrepancies in mechanistic speculations have also led to a variety of rate equations for hydroformylation processes. 

It should be noted that these results with the cobalt carbonyl phosphine catalysts may not apply over a wide range of conditions. At milder conditions of lower temperature and low catalyst concentration, the conversion of Co2(CO)8 to HCo(CO)3PR3 is only partially completed, even with up to 5/1 ratios of P/Co (22). 

In contrast to rhodium and iridium, monoatomic cobalt has not been investigated extensively as a hydrosilylation catalyst, though one report discusses the use of cobalt phosphine complexes.54... 

Rhodium-phosphine catalysts are unable to hydroformylate internal olefins, so much that in a mixture of butenes only the terminal isomer is transformed into valeraldehydes (see 4.1.1.2). This is a field still for using cobalt-based catalysts. Indeed, [Co2(CO)6(TPPTS)2] -i-lO TPPTS catalyzed the hydroformylation of 2-pentenes in a two-phase reaction with good yields (up to 70%, but typically between 10 and 20 %). The major products were 1-hexanal and 2-methylpentanal, and n/i selectivity up to 75/25 was observed (Scheme 4.12). The catalyst was recycled in four mns with an increase in activity (from 13 to 19 %), while the selectivity remained constant (n/i = 64/36). 

Derivatives of the steroids androstene and pregnene have been transformed directly into A-acyl amino acids by an orthogonal catalysis procedure, utilizing [RhCl(nbd)]2 and Co2(CO)8 (Scheme 11). The rhodium phosphine catalyst (generated in situ in the presence of syn-gas and phosphine) affects hydroformylation of the internal olefin to generate aldehyde. In the presence of Co2(CO)8, A-acyl amino acids are obtained as the major products. An unstable amido alcohol intermediate, formed by reaction of the amide with aldehyde, is proposed to undergo cobalt-catalyzed GO insertion to yield the desired A-acyl amino acid. 

It should be recognized that the stability of cobalt complexes under carbon monoxide can be enhanced by the addition of ligands, as is the case for phosphine-modified cobalt hydroformylation catalysts (57, 58). The stability will also probably depend on properties of the solvent employed. Nevertheless, the plot shown in Fig. 4 appears to be quite useful for assessing long-term cobalt stability under H2/CO in the absence of strongly coordinating solvents or ligands. 

Na5[Co+(CO)3(19)2]5 was used as catalyst for the hydroformylation of 1-hexene and 1-octene in a two phase system without leaching of cobalt into the organic phase.122 The products obtained were almost exclusively aldehydes (4-38%) and very little (0.4-3%) or no alcohol formation122 in contrast with cobalt/phosphine catalysed hydroformylation in organic solvents which give alcohols. The n/i ratios of the aldehydes were low (1.1-2.5),122 however, and never approached that expected for a phosphine modified cobalt catalyst in non-aqueous media324,325,393 (see Table 8). 

Higher n/b ratios in cobalt-modified catalysts are apparently achieved as a result of the phosphine presenting more steric bulk to the insertion reaction of the alkene. The effect is predominately steric, since there is little correlation with regiochemistry and phosphine bacisity. A combination of electronic (Xi) and steric (cone angle 0) effects provide a more rational explanation of the increase in nib ratio with added phosphines.16,17... 

An interesting example of 1,2-diketone reduction using methods other than metal/phosphine catalysts is the use of a cobalt complex, in combination with quinine, for the reduction of benzil218. In this example the product was formed in 78% e.e. (Scheme 43). 

Cobaltocenium calix[4]arene receptors, characteristics, 12,475 Cobaltocenium-metallacarborane salts, preparation, 3, 23 Cobaltocenium receptors, characteristics, 12, 474 Cobalt phosphines, as supports, 12, 683 Cobalt-platinum nanoparticles, preparation, 12, 74 Cobalt-ruthenium clusters, as heterogeneous catalyst precursors, 12, 768... 

A breakthrough occurred in the mid-seventies when Union Carbide and Celanese introduced Rh/phosphine catalysts in commercial processes. This catalyst is based on the work by Wilkinson s group he received the Nobel prize for his work in 1973. Rhodium-based catalysts are much more active than cobalt catalysts and, under certain conditions, at least for 1-alkenes, they are also more selective. The processes for the hydroformylation of higher alkenes (detergent alcohols) still rely on cobalt catalysis. A new development is the use of water-soluble complexes obtained through sulphonation of the Ligands (Ruhrchemie). 

Table 5.2. Hydroformylation of propene in 2-ethylhexanol with phosphine-substituted cobalt hydrocarbonyl catalyst, HCo(CO)3Ph (Ph = organic phosphine) and synthesis gas of 2 1 H2-to-CO ratio at 50 atm and 130° C in semi-batch reactor.

Example 5.3. Hydroformylation of 1-pentene with phosphine-substituted cobalt hydrocarbonyl catalyst [2], Results of hydroformylation of 1-pentene in a semi-batch reactor are shown in Table 5.5. 

Example 6.5. Olefin hydroformylation with phosphine-substituted cobalt hydrocarbonyl catalyst [30], The pathway 6.9 of olefin hydroformylation with the "oxo" catalyst, HCo(CO)4, has been shown in Example 6.2 in Section 6.3. For phosphine-substituted catalysts, HCo(CO)3Ph (Ph = organic phosphine), the pathway olefin — aldehyde is essentially the same. However, these catalysts also promote hydrogenation of aldehyde to alcohol (Examples 7.3 and 7.4) and of olefin to paraffin (Example 7.5). Moreover, straight-chain primary aldehydes under the conditions of the reaction undergo to some extent condensation to aldol, which is subsequently dehydrated and hydrogenated to yield an alcohol of twice the carbon number (e.g., 2-ethyl hexanol from n-butanal see Section 11.2). The entire reaction system is... 

Example 7.6. Olefin hydroformylation with phosphine-substituted cobalt hydrocarbonyl catalyst [7], The overall reaction system of olefin hydroformylation with a phosphine-substituted cobalt hydrocarbonyl catalyst to produce alcohol, paraffin, and a heavy alcohol has been shown in Example 6.5 (Section 6.5) ... 

If the amounts of the catalyst ingredients (cobalt, phosphine, and base) are increased by the same factor without change in pressure and H2-to-CO ratio, the increase in phosphine concentration uncompensated by an increase in CO pressure shifts ligand exchange equilibrium toward HCo(CO)3Ph. Without base, this shift is at the expense of the more active HCo(CO)4, producing an apparent reaction order lower than one in "catalyst." In the presence of base, the shift is mostly at the expense of the inactive Co(CO)4, resulting in an apparent order higher than one. 

Example 8.11. Hydrcformylation with phosphine-substituted cobalt hydrocarbonyl catalyst. The phosphine-substituted cobalt hydrocarbonyl catalyst used for hydro-formylation of olefins has been described in Section 8.2 (see network 8.13). The principal reaction... 

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