No 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 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).

Anhydrous H[BH (CN) ] crystallizes from acidic aqueous solutions of the dicyanodihydridoborate anion. The formation of H[BH (CN) ] is surprising as the protonation of nitriles requires strongly acidic and anhydrous conditions but it can be rationalized based on theoretical data. In contrast, [BX(CN) ] (X=H, F) gives the expected oxonium salts (H O)[BX(CN) ] while (H O)[BF (CN) ]/H[BF (CN) ] is unstable. H[BH (CN) ] forms chains via N-H⋅⋅⋅N bonds in the solid state and melts at 54 °C. Solutions of H[BH (CN) ] in the room-temperature ionic liquid [EMIm][BH (CN) ] contain the [(NC)H BCN-H⋅⋅⋅NCBH (CN)] anion and are unusually stable, which enabled the study of selected spectroscopic and physical properties. [(NC)H BCN-H⋅⋅⋅NCBH (CN)] slowly gives H and [(NC)H BCN-BH(CN) ] . The latter compound is a source of the free Lewis acid BH(CN) , as shown by the generation of [BHF(CN) ] and BH(CN) ⋅py.

Dependence of electronic properties and reactivity of closo-borates with size and halogen substituent was investigated.

Pentafluoroethyltricyanoborate frameworks of rare-earth metal ions of the general formula [Ln{CFB(CN)}(OH)] (Ln = La, Eu, Ho; n = 0, 3; [Ln1(OH)]) were synthesized using the oxonium salt (HO)[CFB(CN)] ((HO)1) and lanthanide chlorides LnCl·nHO as starting compounds. Single-crystals of [La{CFB(CN)}] ([La1]) are obtained from the room temperature ionic liquid (RTIL) [EMIm]1 using either a ionothermal approach or by recrystallization of anhydrous microcrystalline [La1] that is obtained from reactions in aqueous media after drying in a vacuum. Removal of water from [Ln1(OH)] (Ln = Eu, Ho) to give microcrystalline [Ln1] is achieved in a vacuum at elevated temperatures. All compounds were characterized by vibrational and NMR spectroscopy, thermogravimetry, and elemental analysis. The structures of the three-dimensional coordination polymers [Eu1(OH)] and [La1] were elucidated by single-crystal X-ray-diffraction. According to powder diffraction studies on anhydrous [Ln1] (Ln = La, Eu, Ho), the three compounds are isotypic. A study of the photoluminescence properties reveals that both Eu compounds, [Eu1] and [Eu1(OH)], are strongly luminescent, the emission of the anhydrous framework being significantly more intense than the one of the hydrate. The Eu-compounds benefit from a sensitizer effect of the anion. In contrast, the Ho-containing framework [Ho1] exhibits separate chromophores and a strong reabsorption of the fluorescence by the Ho ions.

Wasserfreies H[BH 2 (CN) 2 ]k ristallisiert aus sauren wässrigen Lçsungen des Dicyanodihydridoborat-Anions.

The reactivity of [Ni(iPr2Im)4(µ‐COD)] 1 (iPr2Im = 1,3‐diisopropyl‐imidazolin‐2‐ylidene, COD = 1,4‐cyclooctadiene) in Hiyama‐ and Negishi‐type cross‐coupling reactions as well as the synthesis of several novel nickel fluoroaryl alkyl complexes is reported. Hiyama coupling of 1.1 equiv. perfluoroaromatics and 1 equiv. PhSi(OR)3 (R = Me, Et) with 5 mol‐% of 1 as catalyst leads to the C–C coupling product ArF–Ph in good to fair yields. In presence of the additive NMe4F alkoxy transfer from PhSi(OR)3 to the perfluoroarene occurs to yield ArF–OR and PhSiF(OR)2. Negishi cross‐coupling between C6F6 or C7F8 (1 equiv.), diorganozinc reagents [ZnR2] (R = Me, Et) (2.1 equiv.) and 5 mol‐% 1 as the catalyst in toluene at 115 °C leads to ArF–R only in traces. However, NMR experiments revealed that nickel alkyl complexes are readily formed from the reaction of trans‐[Ni(iPr2Im)2(F)(ArF)] with [ZnR2] (R = Me, Et). In course of these investigations, a series of novel nickel alkyl complexes trans‐[Ni(iPr2Im)2(R)(ArF)] (R = Me, ArF = C6F5 2, C7F7 3, C12F9 4; R = Et, ArF = C6F5 5, C7F7 6, C12F9 7) have been synthesized in stoichiometric reactions starting from trans‐[Ni(iPr2Im)2(F)(ArF)] (ArF = C6F5, C7F7, C12F9) and [ZnR2] (R = Me, Et) in thf at –78 °C. As these nickel alkyl complexes 2–7 are stable at room temperature in solution for several days with respect to reductive elimination, their thermal stability was investigated. Heating trans‐[Ni(iPr2Im)2(Me)(C6F5)] 2 for 24 hours at 100 °C leads to 91 % unreacted complex 2 and only traces of reductive elimination product, i.e. C6F5Me, are formed. Furthermore, the nickel ethyl complex trans‐[Ni(iPr2Im)2(Et)(C6F5)] 5 is also very stable, even with respect to β‐hydride elimination. After heating this complex to 100 °C for 24 hours there is still 26 % unreacted 5 left.

In recent years, salts of the hydridotricyanoborate anion [BH­(CN)3]− (MHB) have become readily available. In spite of the unusually high stability of the MHB anion, it can be used as a valuable starting material for the preparation of selected tricyanoborates, for example, the boron-centered nucleophile B­(CN)3 2–. A further unprecedented example is the hydroxytricyanoborate anion [B­(OH)­(CN)3]− that is accessible by oxidation of (H3O)MHB with elemental bromine in water. The Brønsted acid (H3O)­[B­(OH)­(CN)3] was isolated as a crystalline solid. It serves as a versatile starting material for the synthesis of coordination compounds, metal salts, and ionic liquids. The [B­(OH)­(CN)3]− anion shows a rich coordination chemistry and a high tendency to form hydrogen-bonded motifs as demonstrated by a series of salts with different types of cations. Furthermore, the [B­(OH)­(CN)3]− anion itself serves as starting material for new tricyanoborates such as the unusual trianion [B­{OB­(CN)3}3]3– and the silylated anions [B­(OSiR3)­(CN)3]− (R = Me, Et, Ph). Some of these follow-up products have been characterized by single-crystal X-ray diffraction, e.g., [nBu4N]3[B­{OB­(CN)3}3] and [nBu4N]­[B­(OSiPh3)­(CN)3].