PNNL

Abstract

High-yield syntheses up to molar scales for salts of [BH(CN)3]– (2) and [BH2(CN)2]– (3) starting from commercially available Na[BH4] (Na5), Na[BH3(CN)] (Na4), BCl3, (CH3)3SiCN, and KCN were develop-ed. Direct conversion of Na5 into K2 was accomplished with (CH3)3Si¬CN and (CH3)3SiCl as a catalyst in an autoclave. Alternatively, Na5 is converted into Na¬[BH{OC(O)R}3] (R = alkyl) that is more reactive towards (CH3)3SiCN and thus provides an easy access to salts of 2. Some reaction intermediates were identi¬fied, e.g. Na-[BH(CN)¬{OC(O)Et}2] (Na7b) and Na[BH(CN)2{OC(O)Et}](Na8b). A third entry to 2 and 3 uses ether adducts of BHCl2 or BH2Cl such as the commercial 1,4-dioxane adducts that react with KCN and Me3SiCN. Alkali metal salts of 2 and 3 are starting materials for various inorganic and organic salts, e.g. low viscosity ionic liquids (ILs). [EMIm]3 is the lowest vis¬co¬us and highest conducting non-protic IL known with 10.2 mPa·s and 32.6 mS·cm–1 at 20 °C. The ILs are thermally, chemically, and electro¬¬chemically robust. These properties are crucial for applications in electro-chemical devices, e.g. dye-sensitized solar cells (Grätzel cells).