Reduction of cobalt complexes by carbon monoxide and synthesis of mono- and bis-organometallic derivatives

Abstract

Cobalt(III) complexes of the type [Co^III(chel)(OH)(H₂O)], where chel is a tetradentate conjugated chelating ligand, react in water with CO yielding, in the pH range 4–13, [Co^II(chel)]. Formation of [Co^III(chel)(CO₂H)(H₂O)] through nucleophilic attack of OH– on the intermediate [Co^III(chel)(CO)(OH)] is assumed. The carboxy-derivative decomposes yielding CO₂ and [Co^I(chel)]^– species which, in turn, gives [Co^II(chel)] by different reaction paths depending on pH of the solution. The same mechanism operates for the complex with the 2,3,9,10-tetramethyl-1,4,8,11-tetra-azaundeca-1,3,8,10-tetraen-11-ol-1-olato anion(tn) up to pH 8. In more alkaline solution (pH 13) the corresponding carbonyl derivative [Co^I(chel)(CO)] can be isolated. With all chel complexes investigated the reaction in alkaline solution appears to be autocatalytic. Mono- and di-organometallic derivatives can be prepared by the same reaction in the presence of organic halides.