(I) Zinc aqua and alkoxide complexes: Models of zinc enzymes. (II) Estimation of the Bronsted acidity of aquatris(perfluorophenyl)borane

I. A series of zinc alkoxide complexes, [$TpBut,Me$]ZnOR, were synthesized as models for liver alcohol dehydrogenase (LADH). Thermodynamic measurements show that steric bulk and electronic withdrawing substituents destabilize these alkoxides towards hydrolysis. Density functional theory (DFT) calculations suggest that the steric effect is caused by the bulky [$TpBut,Me$] ligand, and the electronic effect results from Zn-OAr bond dissociation energies being more sensitive to substituents than H-OAr bond energies. The difference between Zn-OAr and H-OAr substituent effects can be explained by the greater ionic character of Zn-OAr bonds. DFT calculations indicate that while the overall energy of hydrolysis is different for zinc cobalt and cadmium alkoxides, the substituent effect is the same.; The zinc alkoxides [$TpBut,Me$]ZnOR are functional models of LADH as they are able to transfer hydride to para-nitrobenzaldehyde. Hydride transfer from the B-H moeity of the [$TpBut,Me$] ligand is also observed. This reaction is not biologically relevant, but it is a novel form of reactivity for this ligand system.; Protonation of a zinc hydroxide to form the zinc aqua complex {lcub}[$TpBut,Me$]ZnOH₂{rcub}[HOB(C₆F₅)₃] models the catalytic cycle of carbonic anhydrase. In support of the proposed enzyme mechanism, the aqua complex does not react with CO₂. The hydrogen bond between the cation and anion is disrupted by donating solvents, allowing destroys the [$TpBut,Me$] ligand and results in the formation of a small yield of [$TpBut,Me$]ZnH.; II. The Brønsted acidity of (C₆F ₅)₃B(OH₂) in acetonitrile was estimated to be 8.4 through a combined experimental and computational study. A kinetic analysis of ligand dissociation from (C₆F₅)₃B(OH ₂) and (C₆F₅)₃B(NCMe) shows that the barrier for addition of MeCN is 2.8 kcal mol−1 greater than that for the addition of water.