Triorganyl‐ and Diorganyloxozirconium Hydridoborates – Synthesis and Structures

The reactions of Zr(OBu)(4) and Zr(OEt)(4) with H3B center dot THF in THF led to HB(OR)(2) and B(OR)(3), but no zirconium tetrahydroborate [(RO)(4) Zr-n(BH4)(n)] could be isolated. On the contrary, the reactions of [tBu(3)CO](4-n)ZrCln and [tBu(3)SiO](4-n)ZrCln with LiBH4 generated the tetrahydroborates [(RO)(3)Zr(BH4)] and [(RO)(2)Zr(BH4)(2)]. These can be used to produce by hydroborate exchange dihydridodiorganyl borates [(RO)(4-n)Zr(H2BC8H14)(n)] and byproducts. The structures of the new zirconium hydridoborates have been determined by X-ray crystallography. Compound [(tBu(3)CO)(3)Zr(H2BC8H14)] shows site-disordered dihydroborate units with agostic Zr-H-C interactions, while [(tBu(3)SiO)(2)Zr(H2BC8H14)(2)] is quite symmetric (C-2/c). The corresponding tetrahydridoborates possess in most cases mu(3)(1)-bonded ZrH3BH groups.