Synthesis of Known and Previously Inaccessible Poly(pyrazolyl)Borates under Mild Conditions

Abstract

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.

“Homoleptic” Tetracoordinate Boron Compounds

“…This would result in several problems such as difficulty in control of the reaction stoichiometry, the emission of flammable hydrogen gas at high temperature, limited functional group compatibility, and the inapplicability when multisubstituted electron-deficient pyrazoles are employed. To address this issue, Ramírez de Arellano and Olmos developed a practical and direct method for the preparation of poly­(pyrazolyl)­borate ligands under very mild conditions . In detail, the chosen pyrazoles were deprotonated by sodium hydride to form the corresponding sodium pyrazolides.…”