Zinc Pyrazolylborate Complexes Relevant to the Biological Function of Carbonic Anhydrase

The structure and function of the active center of the zinc enzyme carboanhydrase—the biological counterpart to hemoglobin, which transports CO2 from the body—are quite well known, though none of the postulated intermediates of the catalytic cycle has been characterized. With the labile hydrogencarbonato complex 1, formed from the analogous hydroxo complex by the reversible uptake of CO2, a model compound for one of the key steps in the catalytic cycle is now obtained for the first time.