Anionic zirconium and hafnium borohydride complexes

Zirconium and hafnium tetrachlorides react with NaBH₄, in dimethoxyethane (DME) to give Na(DME)₃]M(BH₄)₅]. These compounds react with Bu₄NBH₄ and Ph₄PBH₄ to give (R₄E)M(BH₄)₅]. Bidentate and tridentate BH ₄ ^– occur in M(BH₄)₅]^– according to IR spectroscopy. Data from¹H and¹H-{¹¹B} NMR spectra are consistent with intermolecular exchange of BH₄ ligands in solutions of complexes (I)–(VI). The BH₄groups and the bridging and terminal protons in each BH₄ group equilibrate rapidly. Heating the complexes (I)–(VI) reduces the central atom, releases diborane, and decomposes the outer-sphere cation. The neutral borohydrides M(BH₄)₄, can be prepared by thermolysis of the sodium salts (I) and (II).Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1207–1214, June, 1990.