Synthesis and crystal structure of [UO2(BH4)2(hmpa)2], a novel uranyl complex and the first metal oxoborohydride

Reaction of [UO2Cl2(THF)2]2 with NaBH4 in THF led to the formation of [UO2Cl2−x(BH4) x(THF)n], and addition of hmpa induced the crystallization of [UO2(BH4)2(hmpa)2], whose structure exhibits the bidentate ligation mode of the borohydride ligand; this uranyl borohydride, which is thermally unstable with respect to elimination of borane, is a catalyst in the hydroboration of substituted alkenes by NaBH4.