Tetracyanidoborates with Sterically Demanding Phosphonium Cations – Thermally Resistant lonic Liquids 

Abstract

Abstract The reaction of K[B(CN) 4 ] with [Ph 4 P]Cl, [ n Bu 4 P]Br, [ n BuPh 3 P]Br, or [EtPh 3 P]Cl (Ph = phenyl, n Bu = n ‐butyl, Et = ethyl) affords [Ph 4 P][B(CN) 4 ] ( 1 ), [ n Bu 4 P][B(CN) 4 ] ( 2 ), [EtPh 3 P][B(CN) 4 ] ( 3 ), and [ n BuPh 3 P][B(CN) 4 ] ( 4 ) in high yields. The structures of the compounds 1 – 3 , which contain the tetrahedral [B(CN) 4 ] – ion, were determined by single‐crystal X‐ray diffraction. 1 crystallizes in the tetragonal space group I \bar{4} 2 d (no. 122), a = 12.948(2), c = 29.382(6) Å, Z = 8, R 1( F )/ wR 2( F 2 ) = 0.0335/0.0953; 2 and 3 with orthorhombic symmetry; 2 : space group Pnna (no. 52), a = 18.2187(6), b = 12.0707(3), c = 11.6704(4) Å, Z = 4, R 1( F )/ wR 2( F 2 ) = 0.0489/0.1532; 3 : space group Pnma (no. 62), a = 14.1777(3), b = 13.4214(3), c = 12.3199(2) Å, Z = 4, R 1( F )/ wR 2( F 2 ) = 0.0477/0.1505. The IR, Raman, and NMR spectra as well as thermal data derived from DSC and TGA measurements are reported. Depending on the thermal stability of the phosphonium cation some of the tetracyanidoborates are stable up to ~370 °C with the liquid state having a range of up to 300 K. Such salts could be very useful as weakly coordinating reaction media.