Triorganyl- and diorganyloxozirconium hydridoborates - Synthesis and structures

Abstract

The reactions of Zr(OBu)4 and Zr(OEt)4 with H 3B·THF in THF led to HB(OR)2 and B(OR)3, but no zirconium tetrahydroborate [(RO)4-nZr(BH4) n] could be isolated. On the contrary, the reactions of [tBu 3CO]4-nZrCln and [tBu3SiO] 4-nZrCln with LiBH4 generated the tetrahydroborates [(RO)3Zr(BH4)] and [(RO) 2Zr(BH4)2]. These can be used to produce by hydroborate exchange dihydridodiorganyl borates [(RO)4-nZr(H 2BC8H14)n] and byproducts. The structures of the new zirconium hydridoborates have been determined by X-ray crystallography. Compound [(tBu3CO)3Zr(H 2BC8H14)] shows site-disordered dihydroborate units with agostic Zr-H-C interactions, while [(tBu3SiO) 2Zr(H2BC8H14)2] is quite symmetric (C2/c). The corresponding tetrahydridoborates possess in most cases μ31-bonded ZrH3BH groups. Compounds of the type [(RO)4-nZr(BH4)n] were obtained from the reaction of(RO)4Zr (R = Bu, Et) with H 3B·THF or that of (RO)4-nZrCln(n = 1, 2; R = tBu3C, tBu3Si) with LiBH4. Boryl group exchange with H2BC8H14- leads to (RO)4Zr(H2BC8H14)n with agostic Zr-H-B bonding when n = 1, whereas a symmetric ZrH2B compound results when n = 2. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.