Cobalt metal-carbon bond containing

The generation of the initial metal-carbon bond in the catalytic cycle by reaction of methyl iodide with a metal carbonyl-containing species has been proposed as a key step in both the cobalt (2) and rhodium (4) catalyzed systems. 

Co-enzyme B12 contains cobalt coordinated by a corrin ring and one of the few metal-carbon bonds known in biology (Fig. 5). It assists in a number of enzymatic reactions including the rearrangement reaction where a function-... 

Octahedral complexes of cobalt(III) (d ) are generally diamagnetic 18-electron compounds which are kinetically inert to substitution. This applies to the group of organometallic compounds which includes Vitamin coenzyme, a rare example of a natural product which contains a metal—carbon bond. The human body contains 2-5 mg, mostly in the liver. The coenzyme is implicated in a whole range of biochemical processes of the general type... 

One-electron oxidation of the vinylidene complex transforms it from an Fe=C axially symmetric Fe(ll) carbene to an Fe(lll) complex where the vinylidene carbon bridges between iron and a pyrrole nitrogen. Cobalt and nickel porphyrin carbene complexes adopt this latter structure, with the carbene fragment formally inserted into the metal-nitrogen bond. The difference between the two types of metalloporphyrin carbene, and the conversion of one type to the other by oxidation in the case of iron, has been considered in a theoretical study. The comparison is especially interesting for the iron(ll) and cobalt(lll) carbene complexes Fe(Por)CR2 and Co(Por)(CR2) which both contain metal centers yet adopt... 

The electrosynthesis of metalloporphyrins which contain a metal-carbon a-bond is reviewed in this paper. The electron transfer mechanisms of a-bonded rhodium, cobalt, germanium, and silicon porphyrin complexes were also determined on the basis of voltammetric measurements and controlled-potential electrooxidation/reduction. The four described electrochemical systems demonstrate the versatility and selectivity of electrochemical methods for the synthesis and characterization of metal-carbon o-bonded metalloporphyrins. The reactions between rhodium and cobalt metalloporphyrins and the commonly used CH2CI2 is also discussed. 

The synthesis of metalloporphyrins which contain a metal-carbon a-bond can be accomplished by a number of different methods(l,2). One common synthetic method involves reaction of a Grignardreagent or alkyl(aryl) lithium with (P)MX or (PMX)2 where P is the dianion of a porphyrin macrocycle and X is a halide or pseudohalide. Another common synthetic technique involves reaction of a chemically or electrochemically generated low valent metalloporphyrin with an alkyl or aryl halide. This latter technique is similar to methods described in this paper for electrosynthesis of cobalt and rhodium a-bonded complexes. However, the prevailing mechanisms and the chemical reactions... 

In humans, vitamin Bi2 participates in two reactions only, but they are essential to life. Humans who cannot absorb vitamin Bi2 die of pernicious anemia if untreated (now by injection of the vitamin formerly by eating large amounts of raw liver). Vitamin B]2 contains a cobalt metal ion bound to a porphyrin ring. Cobalt normally forms six coordinate bonds. Besides the four bonds to the nitrogens of the porphyrin, one bond is to a ring nitrogen of dimethylbenzamidine. The final bond is to a cyanide ion in the vitamin, or to the 5 carbon of adenosine in the active coenzyme. 

Cobalt(II) and nickel(II) species reacted with XCH3 to produce intermediate species containing metal-carbon cr-bonds, a process characterised by a small positive A Vthat indicated a dissociative interchange mechanism.295,296 Similar reactions of aquated Cr(II) ions with a series of 10 different aliphatic radicals exhibited an average AV of +4.3+ 1.0cm3mol-1, also evidence for an Id mechanism.297... 

Vitamin B,2 is a cobalt complex. It is essential for good health in man and without it pernicious anaemia will eventually result in death. The vitamin is not synthesised in the human body and has to be obtained from food, mostly meat and dairy products, or micro-organisms. It is the only vitamin which contains a metal ion and furthermore it is often found in vivo with a cobalt-carbon bond - one of Nature s rare organometallic compounds. It is usually used in the laboratory as the beautiful red crystalline solid, which is the cyano-complex. The structure of vitamin B12 was originally determined using this compound, cyanocobalamin, and this is shown in Figure 7.21. The cyano-species is only found in the bodies of people who smoke The cyanide is... 

Complexes Containing Metal-Carbon cr-Bonds of the Groups Iron, Cobalt, and Nickel, Including Carbenes and Carbynes... 

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