Syntheses of the B(8)-hydroxy- and B(8,8')-dihydroxy-derivatives of the bis(1,2-dicarbollido)-3-cobalt(1-)ate ion by its reductive acetoxylation and hydroxylation: molecular structure of [8,8'-μ-CH3C(O)2(1,2-C2B9H10)2-3-Co]0 zwitterion determined by X-ray diffraction analysis
Abstract
Preparative routes to 8-hydroxy-bis(1,2-dicarbollido)-3-cobalt(1-)ate (2) and 8,8'-dihydroxy-bis(1,2-dicarbollido)-3-cobalt(1-)ate (3) ions are reported by the reductive acetoxylation of the parent bis(dicarbollido)cobaltate ion (1) followed by hydrolysis of the intermediates. The essential reagent is acetic anhydride, and strong acids are required as catalysts.
For the hydroxyderivative ion 2 the simultaneous presence of acetic acid brings benefit, whereas it is detrimental for the formation of the dihydroxyderivative 3. Reaction intermediate leading to the dihydroxy derivative is the already reported [8,8'-μ-CH3C(O)2(1,2-C2B9H10)2-3-Co]0 zwitterion.
This compound was adequately characterised for the first time and its molecular structure as determined by X-ray diffraction analysis is presented. Both B-hydroxylated bis(dicarbollido)-ions can be alternatively obtained on the direct hydroxylation of the parent ion by hot 60-80% sulphuric acid.
Optimised synthetic procedures and the main physicochemical properties (MS, TLC, HPLC, 1H- and 11B-NMR) of the species are presented. The probable reaction course of the reductive acetoxylation is discussed.