Synthesis of Some "Cobaloxime" Derivatives:: A Demonstration of "Umpolung" in the Reactivity of an Organometallic Complex
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Donald L. Jameson [1] ; Joseph J. Grzybowski [1] ; Deb E. Hammels [1] ; Ronald K. Castellano [1] ; Molly E. Hoke [1] ; Kimberly Freed [1] ; Sean Basquill [1] ; Angela Mendel [1] ; William J. Shoemaker [1]
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[1] Gettysburg College
Gettysburg College
Borough of Gettysburg, Estados Unidos
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- Localización: Journal of chemical education, ISSN 0021-9584, Vol. 75, Nº 4 (April), 1998, págs. 447-450
- Idioma: inglés
- Texto completo no disponible (Saber más ...)
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Resumen
This article describes a four-reaction sequence for the synthesis of two organometallic "cobaloxime" derivatives. The concept of "Umpolung" or reversal of reactivity is demonstrated in the preparation of complexes. The complex Co(dmgH)2(4-t-BuPy)Et is formed by the reaction of a cobalt (I) intermediate (cobalt in the role of nucleophile) with ethyl iodide. The complex Co(dmgH)2(4-t-BuPy)Ph is formed by the reaction of PhMgBr with a cobalt (III) intermediate (cobalt in the role of electrophile). All the products contain cobalt in the diamagnetic +3 oxidation state and are readily characterized by proton and carbon NMR. The four reaction sequence may be completed in two 4-hour lab periods. Cobaloximes are well known as model complexes for Vitamin B-12 and the experiment exposes students to aspects of classical coordination chemistry, organometallic chemistry and bioinorganic chemistry. The experiment also illustrates an important reactivity parallel between organic and organometallic chemistry.
