Pyrazabole formation by thermolysis of the free acid of the hydrotris(pyrazolyl)borate ion

Abstract

Thermolysis of the free acid of the hydrotris(pyrazolyl)borate ion resulted in one of three product pyrazaboles, depending on the reaction conditions. Melting the acid alone afforded 4,8-trans-(pz)HB(µ-pz)₂BH(pz) (pz = C₃H₃N₂), whilst doing so in the presence of ZrCl₄ resulted in the cis isomer. Melting the acid in a damp HCl atmosphere afforded, on alkaline work-up, the novel oxo-bridged dimeric pyrazabole [(pz)B(µ-pz)₂BO(pz)]₂. The crystal structures of all three pyrazaboles have been determined, and procedures for obtaining each compound in the pure state are described.