Contributions to the Chemistry of Boron, 244 Preparation and Structural Characterization of Lithium Silylborates

Borane triethylamine reacts with lithium triphenylsilanide or lithium tert-butyldiphenylsilanide with formation of lithium (triphenylsilyl)trihydridoborate or lithium (tert-butyldiphenylsilyl)trihydridoborate. Complexation of the lithium cation with various ligands allows the isolation of compounds 1, 2a, and 2b. Trimethoxyborane reacts with lithium trimethylsilanide to form lithium tetrakis(trimethylsilyl)borate 3 and lithium tris(trimethylsilyl)methylborate 4. Mixed single crystals of 3 and 4 show an unexpected coordination of the lithium cation due to the lack of any supporting donor molecule. All silylborates exhibit short Si-B bond lengths compared to tricoordinated silylboranes.