Ferrocene boronic acid receptors

Many of the receptors synthesised interact with a wide variety of anions however, selectivity has been introduced to these systems. Ferrocene-based systems have been shown to detect aqueous phosphate [99] and sulphate [100] ions. Ferrocene boronic acid has been shown to associate with fluoride ion with much stronger binding than to chloride,bromide and other anions [101]. 

The boronic acid 20 reported by Shinkai is a rare example of an enantiopme chiral redox-active receptor." It was found to bind linear and cyclic sugars in aqueous solution at neutral pH due to the reversible reaction between the boronic acid moiety of the protonated ferrocene receptor and the sugar to form a boronate ester. Electrochemical studies revealed that complexation imparted cathodic (ca. - 50 mV) shifts in the Fc /Fc redox couple. Interestingly, moderate enantioselectivity was observed in that (+ ) — 1 bound the linear saccharide D-sorbitol more strongly than L-sorbitol (ATd/AIl = 1-4). However, differences in the electrochemical response to the binding of these enantiomers by 20 were not apparent. 

A related system 70 containing two boronic esters has been developed by Aldridge et al., who observed that the bis-fluoride adduct undergoes a color change from orange to green as the ferrocene is aerobically oxidized to ferrocenium. The same group has also developed a boronic acid with dimethyl amine 71 to act as a ditopic receptor for HF. ... 

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