Organometallic Electrochemical Synthesis

Electrochemistry is an excellent method for the selective and controlled production of reduced B12 forms under potentiostatic control. As alkyl halides or alkyl tosylates react quickly and efficiently with Co(I)-corrins [22,91], which are cleanly generated at controlled electrode potentials near that of Co(II)-/Co(I)-couples, electrochemistry provides a suitable method for the synthesis of organometallic B12 derivatives [87]. 

This methodology has been further expanded by the development of an electrochemical method for the preparation of Co -[(methoxycarbonyl)me-thyl]cob(lll)alamin (49) via the alkylation of cob(II)alamin (23) [113]. The more easily reducible organocob(llI)alamins are known to be reduc-tively cleaved by direct electrochemical reduction or by reduction with cob(l)alamin (40 ) [90]. For 49, in which an acceptor-substituted C-atom is directly bound to the Co-center, a peak potential of reduction of - 0.90 V 

SCE (in DMF, room temperature) was determined [107]. This value is close to that of the redox couple (base-on) Bi2r (23)/Bi2s (40 ) (-0.85 V) and explains the difficulties encountered when preparing 49 via alkylation of 40 [107]. However, under potentiostatic conditions aquocob(III)alamin chloride (4 -Cl ) was submitted to a controlled potential of -0.45 V (vs. 0.1 nCE) to give 23 and after the addition of methylbromoacetate the crystalline alkyl cob(III)alamin was isolated in 75% yield. The reaction was proposed to take place directly via 23 and radical intermediates [113]. 

The alkylation of complete Co(II)corrinoids is thus an efficient and alternative method to the more established synthetic procedures via Co(I)cor-rinoids for the synthesis of reduction-labile Co(III)organocorrinoids ]113, 114]. 

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B. Krautler, B12 Electrochemistry and Organometallic Electrochemical Synthesis. In Chemistry and Biochemistry of B12, ... 

The electrochemical synthesis of organometallics (Lehmkuhl, 1973, 1973a) by conducting the electrolysis at a consumable electrode, e.g. as in the Nalco process (39), is again not readily accommodated in a single formal scheme. 

Scheme 10 Electrochemical synthesis of aUcyl substituted nitroaromatic compounds by the reaction of nitrobenzenes with organometallic reagents...

Tuck, D.G. (1979) Direct electrochemical synthesis of inorganic and organometallic compounds . Pure and Appl. Chem., 51, 2005-2018. 

Said, F.F. and Tuck, D.G. (1982) The direct electrochemical synthesis of organometallic halides of zinc and cadmium with substituted phenyl halides , 7. OrganometaL Chem., 224, 121-124. 

Tuck, D. G., Direct Electrochemical Synthesis of Inorganic and Organometallic Compounds, Pure AppL Chem. 51 [1979] 2005/18. 

Chardon-Noblat S, Cripps GH, Deronzier A, Field JS, Gouws S, Haines RJ, Southway F (2001) Synthesis, structure, and physicochemical characterizations of a new cationic ruthenium(I)-ruthenium(I) tetracarbonyl bipyridine dimer precursor for the electrochemical synthesis of an organometallic ruthenium(O) polymer. Organometallics 20 1668-1675... 

TABLE 8. Electrochemical Synthesis of Organometallic Compoimds by Electrolysis of Complexes... 

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