Reactions with Nickel Carbonyl

In the case of phosphine, especially tri-n-butyl and triphenyl phosphines, an active phosphine complex is formed in the reaction medium via reaction with nickel carbonyl. This complex is a very active species provided that the optimum concentration of phosphine is used. Low phosphine concentration results in a loss of the effective nickel concentration through the formation of nickel tetra-carbonyl, nickel metal or nickel iodide. The absolute concentration of phosphine is less important than the P/Ni ratio. In addition to form the stable Ni-P catalyst, the phosphine has to compete with other ligands in the reaction mixture for nickel. With high carbon monoxide partial pressure, there is more CO in solution to compete with phosphine favoring the formation of the carbonyl, which is inactive under the reaction conditions. Hence with high carbon mon-... 

Chelating olefins such as cycloocta-1,5-diene, cyclooctatetraene, or dicyclopentadiene have not yielded isolable complexes by direct reaction with nickel carbonyl, probably for reasons outlined in Section III, B. From this it should not be concluded that such complexes are incapable of existence. Using reactions in which nickel carbonyl is not the reactant it has been possible to prepare not only complexes of cyclooctadiene and cyclooctatetraene, but also of simple monoolefins (Section IX). 

Complex [6-37] also undergoes a similar exchange reaction with nickel carbonyl and cobaltocene, equations (6-71) and (6-72). This type of exchange reaction can be given by the general equation (6-73). 

Acetylene-Based Routes. Walter Reppe, the father of modem acetylene chemistry, discovered the reaction of nickel carbonyl with acetylene and water or alcohols to give acryUc acid or esters (75,76). This discovery led to several processes which have been in commercial use. The original Reppe reaction requires a stoichiometric ratio of nickel carbonyl to acetylene. The Rohm and Haas modified or semicatalytic process provides 60—80% of the carbon monoxide from a separate carbon monoxide feed and the remainder from nickel carbonyl (77—78). The reactions for the synthesis of ethyl acrylate are... 

The reaction is initiated with nickel carbonyl. The feeds are adjusted to give the bulk of the carbonyl from carbon monoxide. The reaction takes place continuously in an agitated reactor with a Hquid recirculation loop. The reaction is mn at about atmospheric pressure and at about 40°C with an acetylene carbon monoxide mole ratio of 1.1 1 in the presence of 20% excess alcohol. The reactor effluent is washed with nickel chloride brine to remove excess alcohol and nickel salts and the brine—alcohol mixture is stripped to recover alcohol for recycle. The stripped brine is again used as extractant, but with a bleed stream returned to the nickel carbonyl conversion unit. The neutralized cmde monomer is purified by a series of continuous, low pressure distillations. 

C-C bonds can be formed by reaction with alkyl iodides or more usefully by reaction with metal carbonyls to give aldehydes and ketones e.g. Ni(CO)4 reacts with LiR to form an unstable acyl nickel carbonyl complex which can be attacked by electrophiles such as H+ or R Br to give aldehydes or ketones by solvent-induced reductive elimination ... 

Symmetrical ketones can be prepared in good yields by the reaction of organo-mercuric halides with dicobalt octacarbonyl in THF, or with nickel carbonyl in DMF or certain other solvents. The R group may be aryl or alkyl. However, when R is alkyl, rearrangements may intervene in the C02(CO)g reaction, though the Ni(CO)4 reaction seems to be free from such rearrangements. Divinylic ketones... 

The course of the reaction of phenacyl bromides (39) with nickel carbonyl is markedly dependent on the solvent employed in tetrahydrofuran the products are 1,2-dibenzoylethanes (cf. 40) but in dimethylformamide, 2,5-diarylfurans (41) are obtained in moderate to excellent yield (Scheme 53).90 It is possible that the furan derivatives (41) arise via intermediate fi,y-epoxyketones which can be isolated as products from a number of a-bromo-ketone substrates [cf. 39 and Section II].28... 

The formation of l,3,4-triarylpyrroline-2,5-diones from the reaction of diphenylcyclopropenone and N-sulfinylarylamines with nickel carbonyl has been described earlier (see Scheme 36 in Section IV,A,2).64 In contrast with this result, 2,4,5-triphenyl-3-isothiazolone 1-oxide is produced in this type of process using iron pentacarbonyl, and the analogous cyclohexyl derivative is formed in a nickel carbonyl-mediated reaction (Scheme 115).64 It is probable that metallocyclic species (cf. 93) are intermediates in these transformations. 

In homogeneous solutions NO disproportionation maybe promoted by transition metal complexes, and a variety of mechanisms seem to be available owing to the many possible modes of coordination. One example is the reaction of NO with nickel carbonyl shown in Eq. (35) (76),... 

Another clear example of an acetylene insertion reaction was reported by Chiusoli (15). He observed that allylic halides react catalytically with nickel carbonyl in alcoholic solution, in the presence of CO and acetylene, to form esters of cis-2,5-hexadienoic acid. The intermediate in this reaction is very probably a 7r-allylnickel carbonyl halide, X, which then undergoes acetylene insertion followed by CO insertion and alcoholysis or acyl halide elimination (35). Acetylene is obviously a considerably better inserting group than CO in this reaction since with acetylene and CO, the hexadienoate is the only product, whereas, with only CO, the 3-butenoate ester is formed (15). [See Reaction 59]. 

Carbon monoxide is a colorless, odorless, flammable, almost insoluble, very toxic gas that condenses to a colorless liquid at — 90°C. It is not very reactive, largely because its bond enthalpy (1074 kj-mol ) is the highest for any molecule. However, it is a Lewis base, and the lone pair on the carbon atom forms covalent bonds with d-block atoms and ions. It is also a Lewis acid, because its empty antibonding tr-orbitals can accept electron density from a metal (Fig. 14.39). This dual character makes carbon monoxide very useful for forming complexes, and numerous metal carbonyls are known. An example of this behavior is its reaction with nickel to give nickel carbonyl, a toxic, volatile liquid ... 

Tetrakis[phosphorus(III) chloride] nickel has been prepared by the reaction of nickel carbonyl with phosphorus-(III) chloride at room temperature.1 The synthesis of this compound as described below is based on this method. 

Acrylic acid (CH2=CHC02H, melting point 13.5°C, boiling point 141°C, density 1.045, flash point 68°C) and acrylates were once prepared by reaction of acetylene and carbon monoxide with water or an alcohol, with nickel carbonyl as catalyst. 

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