New Bis(mercaptoimidazolyl)(pyrazolyl)borate Ligands and Their Zinc Complex Chemistry

Nine new tripodal NS2 ligands of the bis(mercaptoimidazolyl)(pyrazolyl)borate type with varying 3‐R‐mercaptoimidazolyl moieties were prepared as their potassium salts. Treatment with zinc salts yielded the complex types L·Zn−Cl, L·Zn−I, L·Zn−ONO2, L·Zn−OClO3 and [L·Zn(imidazole)]ClO4. Attempts at the formation of L·Zn−OH or cationic L·Zn complexes resulted in dismutation and formation of ZnL2 complexes. Hydrolytic destruction yielded one [OZn4(thiooimidazolate)6] complex. The ZnS2NO coordination which is present in the enzyme‐substrate complex of alcohol dehydrogenase could be successfully modelled by an [L·Zn(C2H5OH)]+ complex. The L·Zn−X complexes showed very low catalytic activity in the dehydrogenation of 2‐propanol or the hydrogenation of p‐nitrobenzaldehyde. The new compounds were identified by a total of 12 structure determinations. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)