Synthesis and Characterization of Alkali Metal Hypersilyl Borates

This study focuses on the synthesis of H- and MeO- functionalized alkali metal hypersilyl borates. Consequently, two distinct silanides were used as polysilane frameworks for our chemical manipulations. Tris(silyl)silanide (1) and tris(trimethoxysilyl)silanide (2) react in the same manner with the BH3 ⋅ SMe2 complex to obtain two new alkali metal hypersilyl borates [(R3Si)3SiBH3M (M=alkali metal; R=H, (3), R=MeO, (4 a–c))] in good to excellent yields. NMR spectroscopy for all compounds and single-crystal X-ray crystallography for 3 and 4 a, b enabled a clear structural characterization. Single crystal X-ray analysis of 3 showed a dimeric structure, where two THF-molecules and three hydrides from the BH3-group contribute to the coordination sphere of the lithium atom. Interestingly, crystals suitable for X-ray analysis of 4 a and 4 b showed a solvent-free cluster formation, due to the coordination of the MeO groups. Both species form coordination polymers with different coordination modes depending on the nature of the alkali metal. Attempted hydride abstraction reactions of 3 and 4 with various reagents under the formation of the free boranes proceeded unselectively.