Poly(pyrazolyl)borate ligands have been obtained through
the reaction
of highly reactive haloboranes with in situ formed pyrazolides under
very mild conditions. This versatile synthetic method allows the selective
synthesis of bis-, tris-, or tetrakis(pyrazolyl)borates. Furthermore,
the method is compatible with the use of functional groups on the
heterocyclic moieties of the poly(pyrazolyl)borates that were not
accessible to date. Strongly encumbered sodium and thallium(I) poly(pyrazolyl)borates
with a reduced donating ability have been obtained for the first time.