Organocobalt

Porphyrins and chlorophylls are the most widespread natural pigments. They are associated with the energy-converting processes of respiration and photosynthesis in living organisms, and the synthesis of specific porphyrin derivatives is often motivated by the desire to perform similar processes in the test tube. The structurally and biosynthetically related corrins (e.g. vitamin B,j) catalyze alkylations and rearrangements of carbon skeletons via organocobalt intermediates. The biosyntheses of these chromophores are also of topical interest. 

As mentioned earlier, the possible products of the -complexes include ring-opened structures. This includes isomer 181 and some of its derivatives, for example, 187,188,196,197, 203, and 204, as well as the products of interaction with organoiron, 180,191, and 194, and organocobalt, 199,200, and 201, compounds. They have already been discussed together with the variously characterized V-complexes. Examples of the ring-opening reactions based on the -q- and ri -species are given next. 

B12 and related organocobalt chemistry formation and cleavage of cobalt-carbon bonds. P. J. Toscano and L. G. Marzillo, Prog. Inorg. Chem., 1984, 31,105-204 (677). 

Organocobalt B models axial ligand effects on the structure and coordination chemistry of coba-loximes. N. Bresciani-Pahor, M. Forcohin, L. G. Marzilli, L. Randaccio, M. F. Summers and P. J. Toscano, Coord. Chem. Rev., 1985, 63,1 (263). 

Sutton, P. W. Dahl, L. F. (1967) "The molecular structure of Co3(CO)g CCH3. A tricyclic organocobalt complex containing a metal-coordinated triply bridging aliphatic carbon atom, J. Am. Chem. Soc. 89,261-268. 

This is clo.sely related to the Tertiary radical synthesis" scheme for the preparation of organocobalt porphyrins, in which alkenes insert into the Co—H bond of Co(Por)H instead of creating a new radical as in Eq. (13). If the alkene would form a tertiary cobalt alkyl then polymerization rather than cobalt-alkyl formation is observed. " " " The kinetics for this process have been investigated in detail, in part by competition studies involving two different alkenes. This mimics the chain transfer catalysis process, where two alkenes (monomer and oligomers or... 

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). 

The formulas and names of these organocobalt complexes are usually given in the form [RCo(L4)X], e.g., [vinyl-Co(salen)py]. 

No organocobalt(III) complexes have yet been reported to contain a TT-bonded olefin or acetylene, though the former probably occur as reaction intermediates (see Section VI,B,l,d). In other words, equilibria such as... 

The X-ray data show that organocobalt(III) complexes can exist in the three different stereochemical configurations shown diagrammatically in (XX)-(XXII). 

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