Methylcobalt complexes

Some analogous in vitro reactions of methylcobalt complexes are known, e.g., the methylation of thiols (see Section VI,C,3) and of mercury(II)... 

Reaction with Co(CN)5H . General Considerations. Except for methyl iodide, primary, secondary, and tertiary alkyl iodides formed the corresponding alkanes, accompanied by minor quantities of alkenes, in good yield when added to well-stirred solutions of hydrido complex in a hydrogen atmosphere. Only about 35% of methyl iodide was converted to methane, the remainder forming the stable methylcobalt complex. This apparent preferential competition by pentacyanocobaltate(II) for the methyl radical has been used to prepare the methylcobalt complex (22). 

Alkylation of the Co complex by means of trimethylaluminum produces a cationic methylcobalt complex with an AlMeJ counterion (Eq. 5.36) [142]. 

Simple alkyl and aryl cr-bonded complexes are conveniently prepared by reaction of an alkylating reagent with a halocobalt(II) precursor. All-alkyl systems are rare, but the penta-methylcobaltate(II) anion is known.197 More typically, the coordination sphere of the metal contains additional co-ligands, particularly with P, S, or N donors. Some examples that reflect the style of reactions extant appear below. 

Section V,B A further ESR paper has appeared on the photolysis of a Co (III)-R eobaloxime (78a) and similar observations have been made on the corresponding vitamin Bi2 coenzyme in propanc-1,3-diol (28). Photolysis of a dimethylcobalt (III) chelate gave CH4 and a methylcobalt(II) complex which was believed to disproportionate to a Co(I) and a Co (III) species (191a). 

A large number of methylcobalt(III) complexes with unsaturated ligands has been structurally characterized (74). In compounds where... 

The methyliron(lll) corrphycene complex has been prepared and is stable in the absence of dioxygen the methylcobalt(lll) complex is stable even in the presence of dioxygen. 153 Radiol)ftic reduction occurs at the metal center to produce Fe(ll) and Co(l) corrphycenes, which are also stable upon further radiolytic reduction in neutral solutions they yield species with chlorin-like spectral signatures. In alkaline solutions, species with phlorin-anion-like characteristics are produced. 153 ... 

Only a few syntheses of cobalt-containing metallacycles have been carried out over the period under review. In 1998, Klein and co-workers reported the synthesis of the 18-electron cobalt(i) complex 83, smoothly formed by an aldehyde reaction with a suitable methylcobalt(l) according to Equation (24) <19980M4196>. 

With alkyls not capable of elimination, addition of the alkyl group is possible, e.g.,with methylcobalt carbonyl, which undergoes CO insertion prior to reaction with the diene . The product thus is the acyl complex XLIX. 

Subsequent reactions of the methyl radicals produce the stable organic products ethane and methane. Schrauzer et al. [81] have shown that the ratio of ethane to methane is sensitive to the nature of both the equatorial and axial ligands. In addition, studies of methylcobalt photolyses in DjO showed that methane arises via two competing processes direct abstraction of a hydrogen atom from the equatorial ligand system (Eqn. 46, in which Co (Chelate)L represents the cobalt complex minus one hydrogen atom)... 

By the addition of a phosphine to an alkylcobalt tetracarbonyl, the phosphine-substituted acylcobalt carbonyl can be prepared (182,183). In the case of (methoxycarbonyl)methylcobalt tetracarbonyl as a model compound, some details of the reaction have been revealed. Adding a phosphine to this complex, the kinetically controlled formation of a phosphine-substituted acylcobalt carbonyl is observed that can be converted to the thermodynamically more stable phosphine -substituted derivative. 

As typified by the ethanolysis of (CH3)2Pd(PEt3)2, many solvolyses of metal-carbon bonds are found to be quite complex when studied in detail. Even the generalization that the C—M bond hydrolyzes to give alkane and metal ion is not universally valid. Schrauzer and Windgassen (23) found that a methylcobalt compound with dimethylglyoxime ligands gave methane and methyl chloride in a 3 1 ratio on treatment with hot concentrated hydrochloric acid. Traces of ethane also formed, apparently by thermal decomposition with formation of methyl radicals. Warm concentrated KOH solution decomposed this complex with formation of methane. 

The volatile methylcobalt tetracarbonyl is thermally very unstable, m.p. —44°, and it decomposes at —35° [60]. It is readily oxidiz. The acylation reactions and the role of alkylcobalt carbonyl complexes in catalytic hydroformylation reactions are discussed on p. 334 and in chapter 9 respectively. 

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