Cobalt carbonyl hydride

Remarkably few examples of this type of ring construction are available. The cobalt carbonyl hydride catalyzed hydroformylation of A/,A/ -diallylcarbamates has provided 3-pyrrolidinones (Scheme 61a) (81JOC4433). The pyrrole synthesis shown in Scheme 61b depends on Michael addition of ethyl a-lithioisocyanoacetate to ethyl a-isocyanocrotonate (77LA1174). 

On irradiation it is converted to the cobalt carbonyl hydride 8, as discussed above. The hydride then reacts with the olefin in a reaction sequence containing only thermal steps /10/. 

Many research groups have attributed the isomerization to a series of additions and eliminations of a cobalt carbonyl hydride. However, it has been shown that aldehydes may be found with formyl groups attached to a carbon atom other than the two of the double bond even under non-isomerizing conditions. Piacenti and co-workers (44, 45) studied the hydroformylation of [l-14C]propylene and of a>-deuterated a-olefins. Even for a-olefins with chain lengths up to C6, the formyl group was attached to all possible carbon atoms in the product mixture. However, in the deuterated experiments, deuterium was present only on carbons 2, 3, and a) of the resulting aldehydes. These results were explained by pro-... 

These effects of phosphines are explained by observing that the more strongly basic phosphines will dissociate to the least extent in solution (55, 56), Eqs. (26)-(27). The unsubstituted cobalt carbonyl hydride gives... 

Synonyms Cobalt carbonyl hydride tetracar-bonylhydrocobalt... 

The compound may be prepared in a similar way from cobalt(II) iodide. Also, it may be prepared by thermal decomposition of cobalt carbonyl hydride ... 

Metal derivatives of cobalt carbonyl hydride such as Tl[Co(CO)4], Zn[Co(CO)4]2, or Cd[Co(CO)4]2 are formed upon reaction of cobalt octacarbonyl with these metals in the presence of carbon monoxide under pressure. Reaction with halogens (X) produces cobalt carbonyl halides, Co(CO)X2. 

Cobalt carbonyl hydride, [Co(CO)4H], when treated with butadiene gives a mixture of two isomeric compounds [Co(C4H7)(CO)3] (6,128,165). The same mixture of isomers is formed when Na[Co(CO)4] is treated with crotyl bromide, i.e., a l-bromobut-2-enc/3-bromobut-l-enc mixture (109). These two compounds, [Co(C4H7)(CO)3], have been shown by their nmr spectra to be the two geometrical isomers (XLIII) and (XLIV) of 7r-cro ty 11 ri car bo n y 1 co halt (165). 

In the classical oxo process the catalyst cohalt carbonyl is formed in situ by introducing divalent cobalt into the reactor. High temperature is required for this catalyst formation that gives a mixture of aldehydes and alcohols containing only 60-70% of linear product. A new BASF process using cobalt carbonyl hydride shows improved selectivity and efficient catalyst recovery. The catalyst is prepared by passing an aqueous solution of cobalt salt over a promoter and extracting the catalyst from the water phase with olefin. 

A number of simple and inexpensive materials catalytically promote the cobalt-carbonylation (Reaction 2) in aqueous solution. These include ion-exchange resins, zeolites, or special types of activated carbon. Formation of the active catalyst in a separate reactor is thus economically feasible. The mechanism of this catalysis has not yet been elucidated and seems to differ for each promoter mentioned. After an induction period during which the cobalt fed to the reactor is partially retained by the promoter, fully active materials have absorbed cobalt carbonyl anion Co(CO)4 (ion exchange resins), Co2+ cation (zeolites), or a mixture of Co2+, cobalt carbonyl hydride, and cluster-type cobalt carbonyls (activated carbon). This can be shown by analytical studies (extraction, titration, and IR studies) of active material withdrawn from the reactor. 

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... 

C and a total pressure of 1-300 atm (the pressure of the hydro-formylation reaction), depending on the reactivity of the olefin. After the cobalt carbonyl hydride has passed from the aqueous phase into the organic phase (Reaction 3), stoichiometric hydroformylation (6, 7, 8) takes place (Reactions 4-8). 

Step 4 Decobaltation of the Reaction Product. The product of the hydroformylation reactor containing the catalyst as a mixture of cobalt carbonyl hydride and dicobalt octacarbonyl is fed to the decobaiting section. Mixing the product at 120 °C and 10 atm with a dilute formic acid/ cobalt formate solution in the presence of air decomposes the catalyst (Reaction 9) (12). 

Steric factors are important in reactions of this type. The substituted cobalt carbonyl hydrides HCo(CO)4-n(PPh3)n react with increasing difficulty as n increases (entries 32-34). Another general effect is that a hydridosilane HSiX3 will react more readily (and the product be more robust) as X becomes more electronegative (227,230). This seems to be valid for all oxidative addition processes. 

Carbon monoxide has been found to be surprisingly reactive toward the metals in Group VIII, in both their oxidized and unoxidized states. A sizable number of compounds exist in which one or more CO molecules are attached to a metal atom through the carbon typical of these are nickel tetracarbonyl, Ni(CO)4, iron pentacarbonyl, Fe(CO) cobalt carbonyl hydride, Co(CO)4H platinum carbonyl chloride, Pt(CO)2Cl2 and more complicated molecules such as Co4(CO)i2. 

Cool the reactor to —196° and remove the noncondensable materials by pumping. Allow the reactor to warm to 0° and remove the excess trifluorosilane, tetracarbonyl(trifluorosilyl)-cobalt, and any cobalt carbonyl hydride formed by pumping the volatile products through a — 78° (Dry Ice-acetone mixture) trap into a —196° trap. A dark residue will remain in the reactor consisting of unreacted dicobalt octacarbonyl and decomposition products. Unreacted trifluorosilane will be in the —196° trap. 

Some compounds and their properties are shown in Table 2-9. The iron and cobalt carbonyl hydrides form pale yellow solids or liquids at low temperatures and in the liquid phase begin to decompose above -10 and -20°C, respectively they are relatively more stable in the gas phase, however, particularly when diluted with carbon monoxide. They have revolting odors and are readily oxidized by air. The carbonyl hydride, HMn(CO)5, is appreciably more stable. 

Under pressure of CO and H2, the cobalt catalyst precursor is transformed into cobalt carbonyl hydride, HCo(CO)4. The main steps of the reaction mechanism, first elucidated by D. S. Breslow and R. F. Heck, involve (a) /3-hydrogen transfer to the coordinated olefin, (b) the insertion of CO to form an acyl intermediate, and (c) the hydrogenolysis of the acyl, with formation of the aldehyde product ... 

The oxidative addition of methyl iodide to an unsaturated cobalt carbonyl according to Equation (27) was proposed by Wender, CO insertion gives an acetyl species (28) which is thought to be hydrogenated by cobalt carbonyl hydride or H to yield acetaldehyde [4]. Numerous examples of the oxidative addition of methyl iodide to transition metal complexes with a electron configuration (e.g. Rh Ir ) ate known from the literature [66, 67]. For the carbonytaiion of methanol, the rate has been found to be the oxidative addition of methyl iodide to rhodium(l) [68]. 

Isomerisation of olefins catalysed 11 by palladium and other transi- (34) tion-metal complexes Hydrogenation reaction with 10 cobalt carbonyl hydride as a (29) hydrogenation agent 7r-Complex adsorption in hydrogen 27 exchange on Group VIII transi- (45) tion metal catalysts... 

In solution these carbonyl hydrides act as very weak monobasic acids. The iron and cobalt carbonyl hydrides arc isoelectronic with Ni(CO)4 and have the same tetrahedral structure ... 

Uninegative cobalt is found in sodium tetracarbonylcobaltate(—I), NaCo(CO)4, which is a typical salt with the anion [ 0(00)4] This and the corresponding salts of potassium and calcium are related to cobalt carbonyl hydride (p, 303). 

The first generation of hydroformylation processes (e.g., by BASF, ICI, Kuhlmann, Ruhrchemie) was exclusively based on cobalt as catalyst metal. As a consequence of the well-known stability diagram for cobalt carbonyl hydrides, the reaction conditions had to be rather harsh the pressure ranged between 20 and 35 MPa to avoid decomposition of the catalyst and deposition of metallic cobalt, and the temperature was adjusted according to the pressure and the concentration of the catalyst between 150 and 180 °C to ensure an acceptable rate of reaction. As the reaction conditions were quite similar, the processes differed only in the solution of the problem of how to separate product and catalyst, in order to recover and to recycle the catalyst [4]. Various modes were developed they largely yielded comparable results, and enabled hydroformylation processes to grow rapidly in capacity and importance (see Section 2.1.1.4.3). 

Most catalysts that have been mentioned so far are mononuclear. The few binuclear compounds utilized Co2(CO)8 or phosphinesubstituted derivatives) did not give evidence of any unusual type of binuclear catalysis. However, new products could result with catalysts producing two active centers in close vicinity which would not dissociate in the course of the reaction. The expected difference between mononuclear and binuclear catalysis is shown in the accompanying diagram (52). A series of metal salts of cobalt carbonyl hydride of composition M[Co(C0)4]n (M=Zn, Cd, Hg, n = 2 M = In, = 3) were tested as potential binuclear catalysts. The complex salts are relatively easily accessible Zn[Co(CO)4]2, for instance, may be prepared from cobalt carbonyl, metallic zinc, and CO (at 3000 psi initial pressure) using toluene as the solvent and a temperature of 200°. The compound may also be synthesized directly from metallic cobalt, zinc, and CO... 

Huo et al. studied the structure and energies of cobalt-carbonyl radicals as well as the cationic and anionic homoleptic mononuclear cobalt-carbonlys and the cobalt-carbonyl hydrides.35 The B3LYP functional was applied with all-electron triple- quality basis. They found that most of these complexes prefer less symmetrical structures and minor structural deformations may result in large energetic differences. 

Catalytic Reactions Involving Cobalt Carbonyl Hydride Complexes... 

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