Cobalt carbonyl interaction

Bronstein and co-workers (50) reported an in situ method for the preparation of polymer-cobalt nanocomposites by mixing C02(C0)s with a polyacrylonitrile copolymer or an aromatic polyamide in dimethylformamide (DMF). The cobalt carbonyl interacts with DMF giving the complex [Co(DMF)6l +[Co(CO)4] , which is then converted to nanodispersed Co particles by thermolysis. 

Although the acylcobalt tetracarbonyls react with hydroxide ion under phase-transfer conditions, in the presence of alkenes and alkynes they form o-adducts rapidly via an initial interaction with the ir-electron system. Subsequent extrusion of the organometallic group as the cobalt tetracarbonyl anion leads to a,(J-unsaturated ketones (see Section 8.4). In contrast, the cobalt carbonyl catalysed reaction of phenylethyne in the presence of iodomethane forms the hydroxybut-2-enolide (5) in... 

Acetylation occurs at the 2-position of allene systems (Scheme 8.14). The intermediate 7t-allyl complex breaks down via the nucleophilic displacement of the cobalt carbonyl group by the hydroxide ion to produce the hydroxyketone (7) [ 11 ]. An alternative oxygen-initiated radical decomposition of the complex cannot, however, be totally precluded. The formation of a second major product, the divinyl ketone (8), probably arises from direct interaction of the dicobalt octacarbonyl with the allene and does not require the basic conditions. 

The interaction of Co2(CO)g and Co4(CO)i2 with many common inorganic supports as oxides and zeolites has been reported, and catalysts prepared from cobalt carbonyls have been used in the main reactions in which cobalt is used as active... 

As highly reactive heterocycles, the thietes are well suited for the formation of metal complexes. Takahashi and Dittmer both individually and in collaboration have been involved with the interaction of thietes and iron or cobalt carbonyls. During the thermally or photochemically induced complexation process, ring opening takes place so that the resultant thioacrolein is the actual ligand in the organometallic compound (Scheme i7)/ 3-203,204... 

The structure of the cationic complex [Co2(p,Tj2,772-HC2CH2PEt3)(CO)6]+ has been established by an X-ray diffraction study (Fig. 13).79 The main difference between this type of cationic derivative and the parent propargylium complexes is the absence of any anchimeric assistance from the cobalt to the carbocation center. The cobalt-carbon interaction is replaced by a direct interaction with the heteroatom of the nucleophile. This is reflected in the infrared spectra of the [Co2(/x,r72,T72-HC2CH2nuc)(CO)fi]+ species. The values of the carbonyl stretching bands lie in between those of [Co2(ju.,Tj2,Tj2-HC2CH2OH)(CO)6] and [Co2(m,t, t73-HC2CH2)(CO)6]+. 

The carbonylation of a benzyl halide in the presence of iron pentacarbonyl to give a phenylacetic acid may serve to exemplify the interaction of a metal carbonyl, carbon monoxide, PT catalyst, aqueous sodium hydroxide, and the substrate [79]. Fe(CO)5 is attacked by QOH at the interphase, and the species formed is extracted into the depths of the oganic phase, where it reacts with CO and benzyl halide (Eqs. 13 and 14). This new anion 3 is the actual catalyst. It reacts with a second benzyl halide to give a non-ionic intermediate 4 (Eq. 15). By insertion of CO and attack of QOH, 4 is decomposed to the reaction product under regeneration of 3 (Eq. 16). Thus, the action of the PT catalyst is twofold. Firstly it transports the metal carbonyl anion. More important seems to be its involvement in the (rate-determining) decomposition step. A basically similar mechanism was proposed for cobalt carbonyl reactions [80], which have been modified somewhat quite recently (see below). 

Co2(CO)8 and HCo(CO)4 using HP-IR. A cobalt carbonyl-butadiene complex and an allylcobalt carbonyl species were formed from the reaction of butadiene with Co2(CO)8. Reaction with HCo(CO)4 gradually afforded an alkenyl complex which reacted to form further byproducts. The reaction of cobalt carbonyls with hydrogen or deuterium, and the stoichiometric interaction of the resultant hydride with alkenes has also been studied with HP-IR. Ojima reported HP-IR studies into Co-Rh bimetallic carbonyl catalysts, and observed a CoRh(CO)7 species which was active for hydroformylation-amidocarbonylation. 

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