Chemistry cobalt

Heteroatom transfer in metallacyclopentadienes was first developed in the context of cobalt chemistry in the mid-1970s [27]. Cobaltacyclopentadienes were converted into various five-membered heterocyclic compounds such as pyrrole and thiophene, and into six-mem-bered heterocyclic compounds such as pyridine and pyridone derivatives. In the case of zirconacydopentadienes, the heteroatom compound must bear at least two halide substituents, since the Cp2Zr moiety is re-converted to the stable Cp2ZrX2. Indeed, this is the driving force behind the heteroatom transfer of zirconacydopentadienes. 

Cobalt(II) porphyrins bind dioxygen as would be expected by analogy with the wealth of cobalt(II) complexes which display this property. The initial addition product is invariably a superoxo-type species, confirmed by ESR, IR and X-ray studies.154 Subsequent reaction of the oxygenated complex with more Co11 porphyrin leads to a peroxo-bridged dimer. No X-ray data are available for cobalt porphyrin peroxo-bridged dimers but the formation of such dimers is well established in cobalt chemistry. 

Table 5 gives references to recent general accounts or reviews of aspects of cobalt chemistry not specifically dealt with in this chapter. Other chapters in the present series also contain much detailed information. 

Continuation of Specialist Periodica) Reports on cobalt chemistry, current literature (1978- )... 

The area of alkyne cluster chemistry has been the subject of two previous review articles. The first is concerned largely with alkyne-cobalt chemistry (16), while the second provides a comprehensive, systematic review of alkyne-substituted homo- and heterome-tallic carbonyl clusters of the iron, cobalt, and nickel triads (17). This latter review covers the literature up to the end of 1981. The present work does not set out to be fully comprehensive, but rather reflects the authors own interests in the subject. A number of key examples are... 

Cobalt chemistry, nowadays, might be regarded by some as unfashionable but its importance, both historical and current, is undeniable, as demonstrated by the work outlined in this chapter. Cobalt will always retain its capacity to surprise, as evidenced by the recent serendipitous isolation of both [C0(tmen)(OH2)(H)](NO3)(ClO4) C2H5OH(33), a hydride complex that can be recrystallized from 5 M aqueous HC104 and (34), a carbanionic perchlorate complex isolated from aqueous solution. We await further developments in cobalt chemistry with interest. 

I wish to dedicate this article to David A. Buckingham and Charles R. Clark, two doyens of cobalt chemistry, in gratitude for initiating and fostering my interest in this subject. 

Use of cobalt chemistry that chelates the cyanide directly such as hydroxycobalamin. 

Luengo and Gleason utilized Murai s cobalt chemistry to produce the equatorial C-glycoside 238 in 85% yield, followed by desilylation and conversion of 239 to 241. The final step, standard coupling, then gave 244 the potential GDP-fucose inhibitor (Scheme 45). Several other analogs were also prepared [67]. 

Hilderbrand SA, Lippard SJ (2004) Cobalt chemistry with mixed aminotroponiminate salicylaldiminate ligands synthesis, characterization, and nitric oxide reactivity. Inorg Chem 43 4674 682... 

Cobalt is the only metal in this group whose anionic carbonyl compounds have been investigated in any detail. A carbonyl hydride of rhodium, presumably HRh(CO)4 is formed in low yield as extremely unstable pale yellow crystals by the treatment of rhodium chloride with carbon monoxide in the presence of water and a metal as reducing agent 219). However, this carbonyl hydride of rhodium has not been characterized. Therefore all of the chemistry to be discussed in this section will be cobalt chemistry. 

This is our first example of a bridged compound. The three hydroxides bridge between the two cobalt ions. We name such compounds from left to right and remember to put a yu, in front of the bridging ligands. The oxidation states of the metals could be (III) and (III), (II) and (IV), (I) and (V), or any other combination adding up to 6, but even from our brief exposure to cobalt chemistry, you would probably (and correctly) choose the first altemative. Ihe full name of the compound is... 

Due to the high cost of rhodium, it would be advantageous to develop a process that utilized less expensive metals. To this end, a cobalt-catalyzed ortho-directed halogenation was devised (Scheme 7.85 and Example 7.25) [144]. Similar to the rhodium-catalyzed reactions, the process was successful with NBS and NIS. The cobalt chemistry required elevated temperatures and longer reactions times at a higher catalyst loading (10% vs. 1% for Rh). The yields were not as high as those obtained with rhodium catalysts, and the substrate scope of the reaction was not as broad. 

In conclusion, the investigation of the cobalt chemistry with TIMEN " has established interesting patterns of reactivity that may have an impact in the development of new catalytic reactions in the future. 

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