Phenylboronic hydration

From 2,6-diacetylpyridine dioxime, ferric chloride hydrate, and phenylboronic acid as starting materials the macrocyclic dinuclear iron(ll) complexes 133 can be prepared (Fig. 36). 

From these experiments, Lorand and Edwards concluded that the conjugate base of phenylboronic acid has a tetrahedral, rather than trigonal structure. The dissociation of a hydrogen ion from phenylboronic acid occurs from the interaction of the boron atom with a molecule of water. As the phenylboronic acid and water react, a hydrated proton is liberated, thereby defining the acidity constant K, see Hartley, Phillips and James. This is depicted in heme 5 by considering an explicit water molecule associated with the Lewis acidic boron. The reported pK s of phenylboronic acid fluctuate between 8.7 and 8.9, with a recent in-depth potentiometric titration study refining this value to 8.70 in water at 25°C. ... 

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