Improving the Solubility of Halogenated 1-Ammonio-closo-dodecaborate Anions

Abstract

The partly halogenated and N-alkylated closo-dodecaborates [BClHN(propyl)] and [BBrHNR] (R = ethyl-pentyl) were prepared by alkylation of [BHNH] and subsequent halogenation with elemental chlorine or N-bromosuccinimide. Simple metathesis reactions yielded the [HNMe], [Cmim], [NBu], and Na salts, which were characterized by heteronuclear NMR and IR spectroscopy as well as electrospray ionization mass spectrometry. The crystal structures of the salts [HNMe][BBrHN(ethyl)]·CHCN, [HNMe][BBrHN(propyl)], Na[BBrHN(butyl)], and [HNMe][BClHN(propyl)]·CHCN were determined by single-crystal X-ray diffraction. The [Cmim] salts are thermally stable to temperatures higher than 300 °C. The melting points are between 57 and 80 °C, which classify the [Cmim] salts of [BClHN(propyl)] and [BBrHNR] (R = propyl-pentyl) as ionic liquids. The anions are oxidized only at potentials higher than 2 V versus Fc as determined by cyclic voltammetry. The solubility of the sodium salts in CHCl solution was determined by NMR spectroscopy. With the increasing length of the alkyl chain attached to the ammonio group the solubility is significantly enhanced. A solubility up to 125 mmol/L for Na[BBrHN(pentyl)] in dichloromethane was determined. In addition, the trialkylation of the perchlorinated anion [BClNH] was investigated in detail. A Hofmann elimination was observed to occur at higher temperatures, when alkyl groups with β-hydrogen atoms were introduced. Organic substituents without β-hydrogen atoms gave more stable compounds; however, trialkylation proved to be difficult presumably due to steric hindrance. The crystal structure of the byproduct [PPh][BClN(propargyl)] was determined.

Synthesis and Applications of Perfunctionalized Boron Clusters

“…One of these, [C 6 mim] 2 [B 12 Cl 11 (O- n Pr)] gave a melting point under 100 °C . More recently, the same group showed improved melting properties of dodecaborate-based ionic liquids using [B 12 X 6 H 5 NR 2 ] 2– and [B 12 X 6 H 5 NR 3 ] − anions . These compounds show low (as low as 57 °C) melting points and high (>2 V) electrochemical stability, showing promise not only as ionic liquids but also as electrolytes.…”

“…83 More recently, the same group showed improved melting properties of dodecaborate-based ionic liquids using [B 12 X 6 H 5 NR 2 ] 2− and [B 12 X 6 H 5 NR 3 ] − anions. 110 These compounds show low (as low as 57 °C) melting points and high (>2 V) electrochemical stability, showing promise not only as ionic liquids but also as electrolytes. Notably, [C 6 mim][B 12 Cl 6 H 5 N( n Pr) 3 ] shows a liquid range of over 300 °C between melting (65 °C) and decomposition (371 °C).…”

Zinc Ammonio-dodecaborates: Synthesis, Lewis Acid Strength, and Reactivity

“…Perhalogenated 1-carba-closo-dodecaborate (carborate) anions such as [HCB 11 Cl 11 ] − and [HCB 11 F 11 ] − combine a very low basicity with a high chemical stability 1−5 and have been employed as counterions for numerous reactive cationic species. 6,7 Until recently, 8,9 the synthesis of the parent ion, [CH 12 B 11 ] − , either required the use of the toxic and expensive precursor decaborane (14), B 10 H 14 , 6,10 or it could be obtained by capping of the readily synthesizable [B 11 H 14 ] − anion, albeit in yields rarely higher than 10%. 11,12 As possible alternatives, halogenated 1-ammonio-closo-dodecaborate anions such as [Me 3 NB 12 Cl 11 ] − and [Pr 3 NB 12 H 5 Cl 6 ] − have been developed by Jenne 13,14 and our group.…”

“…Perhalogenated 1-carba- closo -dodecaborate (carborate) anions such as [HCB 11 Cl 11 ] − and [HCB 11 F 11 ] − combine a very low basicity with a high chemical stability − and have been employed as counterions for numerous reactive cationic species. , Until recently, , the synthesis of the parent ion, [CH 12 B 11 ] − , either required the use of the toxic and expensive precursor decaborane(14), B 10 H 14 , , or it could be obtained by capping of the readily synthesizable [B 11 H 14 ] − anion, albeit in yields rarely higher than 10%. , As possible alternatives, halogenated 1-ammonio- closo -dodecaborate anions such as [Me 3 NB 12 Cl 11 ] − and [Pr 3 NB 12 H 5 Cl 6 ] − have been developed by Jenne , and our group . These anions can be prepared in three steps from the readily available dodecaborate dianion, [B 12 H 12 ] 2– , and all steps are suitable for second year undergraduate students with the possible exception of the undeca-chlorination of [H 3 NB 12 H 11 ] − , which requires the use of a pressure vessel at elevated temperatures.…”

Silver Salts of the Weakly Coordinating Anion [Me3NB12Cl11]–

“…Their silver salts are of particular importance and numerous examples were structurally characterized , , , . Recently, the chlorinated closo ‐dodecaborate anion [Me 3 NB 12 Cl 11 ] – was established as a new weakly coordinating anion, which is easily accessible and mimics the properties of the chlorinated 1‐carba‐ closo ‐dodecaborate(–) , , . Wehmschulte et al described the preparation of its silver(I) salt and its crystal structure with acetonitrile as coordinated ligand .…”