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 Tt(R) 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 Tt(R)Zn-X with X = F, Cl, ONO2 and (Tt(t-Bu))(2)Zn. With zinc perchlorate the labile perchlorate complexes Tt(R)Zn-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 [Tt(t-Bu)Zn . EtOH] ClO4-EtOH, p-nitrophenol (NitOH) yielded Tt(cum)Zn-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 [(Tt(t-Bu))(2)Zn-3(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.