Organic Synthesis Catalyzed by Cobalt Complexes with Co-C Bond

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Vitamin B12-dependent enzymes, involving the cobalt species as a catalytic center, mediate various isomerization reactions accompained by carbon-skeleton rearrangements. In this reaction, cobalt-alkyl complex is a key intermediate. In order to simulate the catalytic functions of vitamin B12 as excerted in the hydrophobic active sites of enzymes concerned, we have been dealing with hydrophobic vitamin B12 derivatives which have ester groups in place of the peripheral amide moieties of the naturally occurring vitamin B12. In this work, the carbon-skeleton rearrangements which was applied to the ring-expansion reactions as mediated by hydrophobic vitamin B12 derivatives were investigated under electrochemical conditions.The electrolysis of alicyclic ketones (5,6,7, and 8-membered rings) with a carboxylic ester and a bromomethyl group was carried out in N,N-dimethylformamide in the presence of a catalytic amount of hydrophobic vitamin B12. The ring-expansion reaction largely proceeded at -2.0 V vs.SCE for all the substrates. ESR study showed that the reaction proceed through radical intermediates.We also tried to synthesize a new organometallic catalyst with a cobalt-alkyl complex. An alkylated complex having a cobalt-carbon bond gives an alkyl radical by photolysis. If a dicobalt complex is used, it will give a cyclic compound as a coupling compound of biradical after photolysis. This study focused on developing a new catalyst for prepareing a cyclic copmpound. A new dinucleating ligand, which has schiff base unit liked each other with an ethylene apacer, was synthesized by one-pot reaction of salicylaldehyse, ethylenediamine, and methylenebis (4,4'-salicylaldehyde).