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 developed. Direct conversion of Na5 into K2 was accomplished with (CH3)3SiCN 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 identified, for example, Na[BH(CN){OC(O)Et}2] (Na7 b) and Na[BH(CN)2{OC(O)Et}] (Na8 b). 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 (CH3)3SiCN. Alkali metal salts of 2 and 3 are convenient starting materials for organic salts, especially for low viscosity ionic liquids (ILs). [EMIm]3 has the lowest viscosity and highest conductivity with 10.2 mPa s and 32.6 mS cm−1 at 20 °C known for non‐protic ILs. The ILs are thermally, chemically, and electrochemically robust. These properties are crucial for applications in electrochemical devices, for example, dye‐sensitized solar cells (Grätzel cells).
Diborane(6) dianions with substituents that are bonded to boron via carbon are very reactive and therefore only a few examples are known. Diborane(6) derivatives are the simplest catenated boron compounds with an electron-precise B-B σ-bond that are of fundamental interest and of relevance for material applications. The homoleptic hexacyanodiborane(6) dianion [B2 (CN)6 ](2-) that is chemically very robust is reported. The dianion is air-stable and resistant against boiling water and anhydrous hydrogen fluoride. Its salts are thermally highly stable, for example, decomposition of (H3 O)2 [B2 (CN)6 ] starts at 200 °C. The [B2 (CN)6 ](2-) dianion is readily accessible starting from 1) B(CN)3 (2-) and an oxidant, 2) [BF(CN)3 ](-) and a reductant, or 3) by the reaction of B(CN)3 (2-) with [BHal(CN)3 ](-) (Hal=F, Br). The latter reaction was found to proceed via a triply negatively charged transition state according to an SN 2 mechanism.
The potassium perfluoroalkyltricyanoborates K[C F B(CN) ] [n=1 (1 d), 2 (2 d)] and the potassium mono(perfluoroalkyl)cyanofluoroborates K[C F BF(CN) ] [n=1 (1 c), 2 (2 c)] and [C F BF (CN)] [n=1 (1 b), 2 (2 b), 3 (3 b), 4 (4 b)] are accessible with perfect selectivities on multi-gram scales starting from K[C F BF ] and Me SiCN. The K salts are starting materials for the preparation of salts with organic cations, for example, [EMIm] (EMIm=1-ethyl-3-methylimidazolium). These [EMIm] salts are hydrophobic room-temperature ionic liquids (RTILs) that are thermally, chemically and electrochemically very robust, offering electrochemical windows up to 5.8 V. The RTILs described herein, exhibit very low viscosities with a minimum of 14.0 mPa s at 20 °C for [EMIm]1 c, low melting points down to -57 °C for [EMIm]2 b and extraordinary high conductivities up to 17.6 mS cm at 20 °C for [EMIm]1 c. The combination of these properties makes these ILs promising materials for electrochemical devices as exemplified by the application of selected RTILs as component of electrolytes in dye-sensitised solar cells (DSSCs, Grätzel cells). The efficiency of the DSSCs was found to increase with a decreasing viscosity of the neat ionic liquid. In addition to the spectroscopic characterisation, single crystals of the potassium salts of the anions 1 b-d, 2 d, 3 b and 4 c as well as of [nBu N]2 c have been studied by X-ray diffraction.
Alkali metal tricyanoborates M2B(CN)3 (M = Na, K) are accessible by the reaction of tricyanofluoroborates with alkali metals (i) in liquid NH3 or (ii) in THF-naphthalene. The M2B(CN)3 are versatile starting materials for the synthesis of K[RB(CN)3] (R = Et, C6F5, CH2=CHCH2).
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.