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

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(mu-pz)(2)BH(pz) (pz = C3H 3N2), 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, th e novel ore-bridged dimeric pyrazabole [(pz)B(mu-pz)(2)BO(pz)](2). The crys tal structures of all three pyrazaboles have been determined, and procedure s for obtaining each compound in the pure state are described.