Why does nature use zinc--a personal view.

In this perspective some results from the work by the author's research group on the coordination chemistry of zinc are presented. They are selected so as to highlight the principles which, in the opinion of the author, make zinc unique in its ability to function as the catalytic center for an ever-increasing number of biological processes. In essence, the "non-properties" of zinc are the basis of its success: no redox chemistry, no ligand field effects, no typical coordination numbers or geometries, no stability or inertness of its complexes, no typical "hard" or "soft" characteristics. The chemistry presented here is centered around the "Freiburg Enzyme Model", the pyrazolylborate-ligated zinc-hydroxide complex. The topics discussed in detail include the zinc-water combination, the non-similarity between the Zn-OH and the Zn-SH, Zn-OR or Zn-SR complexes, and the functionalization of CO(2) by zinc-bound nucleophiles. The value of structure correlation analysis for the elucidation of mechanistic details is demonstrated, and the first examples of catalysis by the TpZn-OH complexes are presented.