Cobalt organometallic compounds

Bonding Energetics of Organometallic Compounds Cobalt Inorgatuc Coordination Chemistry Cobalt Organometallic Chemistry Mechanisms of Reaction of Organometallic Complexes. 

Naturally occurring compounds with carbon-metal bonds are very rare The best example of such an organometallic compound is coenzyme Bi2 which has a carbon-cobalt ct bond (Figure 14 4) Pernicious anemia results from a coenzyme B12 deficiency and can be treated by adding sources of cobalt to the diet One source of cobalt IS vitamin B12 a compound structurally related to but not identical with coen zyme B12... 

R. S. Dickson, Organometallic Chemistry of Rhodium and Iridium, Academic Press, New York, 1983, 432 pp. C. White, Organometallic Compounds of Cobalt, Rhodium and Iridium, Chapman Hall, London 1985, 296 pp. 

Certain groups of organocobalt(III) complexes have been dealt with in previous reviews. The organo-corrinoids have been mentioned in all reviews on vitamin B, 2 since 1961, when the coenzyme form was identified as an organometallic compound [see, for example, (79, 178) and references therein]. The literature on the corrinoids is too extensive to be treated comprehensively here and for details and references readers are referred to the book on The Inorganic Chemistry of Vitamin B,2 (136)certain other aspects of the organometallic chemistry of cobalt corrinoids are treated elsewhere (137). The pentacyanides were reviewed in 1967 (105), the DMG complexes (cobaloximes) in 1968 (145), and some aspects of salen, BAE, and related complexes in 1970 (17). 

Second, as a logical development of the first approach, polyphosphazenes have been synthesized that bear phosphine units connected to aryloxy side groups (37). The phosphine units bind organometallic compounds, such as those of iron, cobalt, osmium, or ruthenium (38). In several cases, the catalytic activity of the metal is retained in the macromolecular system (39). A similar binding of transition metals has been accomplished through nido carboranyl units linked to a polyphosphazene chain (40). 

Merox [Mercaptan oxidation] A process for removing mercaptans from petroleum fractions by extracting them into aqueous sodium hydroxide and then catalytically oxidizing them to disulfides using air. The catalyst is an organometallic compound, either a vanadium phthalocyanine supported on charcoal, or a sulfonated cobalt phthalocyanine. Developed by UOP in 1958 and widely licensed by 1994, more than 1,500 units had been built, worldwide. Unzelman, G. H. and Wolf, C. J., in Petroleum Processing Handbook, Bland, W. F. and Davidson, R. L., Eds., McGraw-Hill, New York, 1967, 3-128. 

Table 26. Selected bond enthalpy contributions, D (M-L) and (M-L) kJ mol-1, in organometallic compounds of chromium, manganese, iron cobalt and nickel and related compounds (An asterisk ( ) denotes the average value in a series)...

In 1996, Malacria et al. [139] reported on cobalt-mediated reactions of the related allenynes. Heating the allenyne 222 in the presence of cpCo(CO)2 accompanied by a photochemical activation of this organometallic compound delivered the cross-conjugated trienes 223 (Scheme 15.71). The second triple bond present in the substrate did not participate in the reaction, underlining the higer reactivity of the allene unit. 

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... 

Another possible precursor to conduct free radical reactions is the glycosyl-cobait(III) dimethylglyoximato complex 33 [22,23], These organometallic compounds can readily be prepared by the displacement of the halide atom in 17 with the highly nucleophilic cobalt(I) anion 32. The latter can be generated from the dimeric Co(II) complex 31 under reducing conditions. 

The Bj2 vitamers consist of a group of organometallic compounds that have a common cor-rinoid structure and vary in the substituent bound to the central cobalt atom (Fig. 7) (167,168). The principal naturally occurring Bl2 vitamers are hydroxocobalamin (HOCbl), methylcobal-amin (MeCbl), and adenosylcobalamin (AdoCbl). Cyanocobalamin (CNCbl) is the form commonly used for clinical, pharmaceutical, and food fortification purposes, due to its greater relative stability. 

Chiral Metal Atoms in Optically Active Organo-Transition-Metal Compounds, 18, 151 13C NMR Chemical Shifts and Coupling Constants of Organometallic Compounds, 12, 135 Compounds Derived from Alkynes and Carbonyl Complexes of Cobalt, 12, 323 Conjugate Addition of Grignard Reagents to Aromatic Systems, I, 221 Coordination of Unsaturated Molecules to Transition Metals, 14, 33 Cyclobutadiene Metal Complexes, 4, 95 Cyclopentadienyl Metal Compounds, 2, 365... 

Transition metal-catalyzed cross-coupling reactions between vinyl organometallic compounds and unactivated alkyl halides that can be usually performed with palladium, nickel and cobalt are of particular synthetic interest [37-39]. Recently, the groups of Cahiez [48] and Cossy [49] concurrently reported the first iron-catalyzed reaction of alkenyl Grignard compounds with primary and secondary alkyl halides (X=Br, I) (Scheme 5.15). The two protocols basically differ in the iron source... 

Figure 10-2. Although they are relatively rare in biology, organometallic compounds with metal-carbon bonds are important. An typical example is coenzyme B12. The cobalt is co-ordinated to a tetraazamacrocyclic ligand, and has one axial nitrogen donor heterocyclic ligand and one axial alkyl group. The figure illustrates only the core of the macrocycle and the axial groups.

Catalysts based on organometallic compounds of tin (dibutyltin dilau-rate), lead, bismuth, mercury, and cobalt are also frequently employed. As a general rule they are not selective they catalyze the reaction of isocyanates with both hydroxyl groups and water. 

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