Cobalt atom formal oxidation states

Brookhart s group has discovered a new hydrido organocobalt complex in which the cobalt atom is in a high oxidation state. They thus reported a rare example of an organometallic cobalt derivative with a +v formal oxidation state for the cobalt center 10. This species contained additional silyl ligands that stabilized such high oxidation state complexes. These species were remarkably resistant toward reductive elimination. The 2.28 A H-H and the... 

The blood-red liquid obtained by treating cobaltocene with perfluoro-methyl iodide 112) could be formulated as (IX) with the cobalt atom formally in a + 3 oxidation state, rather than (X) with two /x bonds, but an X-ray study would be required to settle this point, as well as whether the CF3 group is in the endo or exo position. 

Figure 26.6 Vitamin B12 (a) a corrin ring showing a square-planar set of N atoms and a replaceable H, and (b) simplified stmcture of B12. In view of the H displaced from the corrin ring, the Co-C bond, and the charge on the ribose phosphate, the cobalt is formally in the - -3 oxidation state. This and related molecules are conveniently represented as r...

These derivatives (Type B) are at least formally prepared by the insertion of a fragment into a M-N bond to yield a new M-X-N unit. Such species have been suggested as possible intermediates in the insertion of an oxygen atom into a G-H bond by cytochrome P-450. Several of these derivatives have formally had a carbene fragment inserted into a M-N bond. Such derivatives include a Ni derivative and a cobalt(III) species that has undergone two such insertion reactions. Other species represent the formal reaction of a vinylidene with iron(III) (two different crystalline forms). This iron derivative has an intermediate-spin state. Other complexes result from the insertion of a nitrene or an oxene This last derivative can also be considered to be a porphyrin N-oxide derivative and the structure of a free base species of a porphyrin N-oxide has also been reported". Appropriate stereochemical parameters for the members of this class are found in Table IX. 

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