Bridged (β-alkoxyalkyl)CoIII(salen) complexes by intramolecular alkoxycobaltation of unactivated alkenes: new models for coenzyme B12
| Autor: | Juul L. van der Baan, Martinus W.G. de Bolster, Wilberth J. J. Smeets, Jan H. Laan, Sijbe Balt, Anthony L. Spek, Gerhard W. Klumpp, R. Blaauw, Irene E. Kingma |
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| Rok vydání: | 2000 |
| Předmět: | |
| Zdroj: | Journal of the Chemical Society, Perkin Transactions 1. :1199-1210 |
| ISSN: | 1364-5463 1470-4358 |
| DOI: | 10.1039/b000196l |
| Popis: | CoII(salen) derivatives (salen = {N,N′-ethylenebis[salicylideneaminato]}) whose ethanediyl moiety carries an alkenyl side-chain R [R = prop-2-en-1-yl (6a), 2-methylprop-2-en-1-yl (6b), but-2-en-1-yl (6c), but-3-en-1-yl (6d)] react with oxygen and alcohols to give organocobalt(III) complexes containing a β-alkoxy-substituted three- or four-carbon bridge between cobalt and the equatorial ligand. NMR and UV–VIS spectroscopic studies show that product formation is a three-stage process involving (1) oxidation of cobalt(II) to produce an (alkoxo)cobalt(III) complex, (2) intramolecular interaction of cobalt(III) with the alkenyl double bond to yield a carbocationic intermediate, and (3) nucleophilic attack by the alcohol. In the case of cobalt(II) complex 6e (R = 3-methylbut-3-en-1-yl), the major product is bridged β-methylene organocobalt(III) complex 10, demonstrating that proton loss competes with addition of alcohols when the intermediate organocobalt(III) species has a substantial degree of tertiary carbocation character. Application of the alkoxycobaltation reaction to 6d and ethane-1,2-diol afforded bridged [β-(2-hydroxyethoxy)alkyl]Co(salen) complex 20, a simple model for coenzyme B12 with a built-in substrate. The molecular structure of 20 has been determined by X-ray diffraction methods. |
| Databáze: | OpenAIRE |
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