Sulfur-Rich Zinc Chemistry: New Tris(thioimidazolyl)hydroborate Ligands and Their Zinc Complex Chemistry Related to the Structure and Function of Alcohol Dehydrogenase

The 1-substituted tris(2-thioimidazolyl)hydroborate ligands TtR were prepared as the potassium salts from KBH4
and the corresponding 1-R-2-thioimidazole for R = t-Bu and C6H4-p-CH(CH3)2 (Cum). Their reactions with zinc
salts yielded the tetrahedral complexes TtRZn−X with X = F, Cl, ONO2 and (Ttt-Bu)2Zn. With zinc perchlorate
the labile perchlorate complexes TtRZn−OClO3 were obtained. They served as starting materials for the
incorporation of substrates which are relevant for the chemistry of horse liver alcohol dehydrogenase:  Ethanol
led to [Ttt-BuZn·EtOH] ClO4·EtOH, p-nitrophenol (NitOH) yielded TtCumZn−ONit. Pyridine-2-carbaldehyde and
salicylic aldehyde were incorporated as N(pyridine) and O(phenolate) coligands with possible additional O(aldehyde)
coordination. Substituted pyridyl methanols (R−PyCH2OH) yielded the trinuclear complexes [(Ttt-Bu)2Zn3(R−PyCH2O)2] (ClO4)2 with bridging Tt and pyridylmethoxide ligands. Preliminary experiments on the functional
modeling of alcohol dehydrogenase have shown that TtZn complexes promote both the dehydrogenation of
2-propanol and the hydrogenation of pentafluorobenzaldehyde.