Synthesis and Properties of the Tetrakis(trifluoromethyl)borate Anion, [B(CF3)4]−: Structure Determination of Cs[B(CF3)4] by Single-Crystal X-ray Diffraction

Abstract

Salts of the tetrakis(trifluoromethyl)borate anion, M[B(CF3)4], M=Li, K, Cs, Ag, have been prepared by two different routes for the first time. The colorless compounds are thermally stable up to 425 C (Cs salt) and soluble in anhydrous HF, water, and most organic solvents. Single crystals of Cs[B(CF3)4] were grown from diethyl ether by diffusion of CH2Cl2 vapor into the solution. The molecular structure was obtained by single-crystal X-ray diffraction. Crystal data: rhombohedral space group R3m (no. 160); a =7.883(1), c=13.847(4) A: V=748.2 A3; Z=3; T=150K; R1=0.0118, wR2=0.0290. The internal bond parameters of the [B(CF3)4] ion were compared to those of the C(CF3)4 molecule. Due to a disorder of the anions in the cesium salt, it is not possible to distinguish between T and Td symmetry by X-ray diffraction experiments alone. However, a comprehensive IR and Raman study demonstrated that in the potassium and cesium salt as well as in aqueous solution, the anion exhibits T symmetry with all CF3 groups rotated off the staggered position required for Td symmetry. The vibrational study is supported by DFT calculations, which provide, in addition to the equilibrium structure and vibrational wavenumbers, estimates of IR and Raman band intensities. The anion is resistant against strong oxidizing (e.g., F2) as well as reducing agents (e.g., Na) and is not affected by nucleophiles like C2H5O or electrophiles such as H3O+. It is very weakly coordinating, as demonstrated by the low-equilibrium CO pressure over the [Ag(CO)x][B(CF3)4] (x=1, 2) co-adducts and the formation of [Ag(CO)x][B(CF3)4] (x=3,4) at higher CO pressure. The 11B, 13C, and 19F NMR data as well as the structural parameters of the anion are compared with those for other borates containing F, CN, and CF3 ligands.

Synthesis and NMR spectroscopic investigation of salts containing the novel [Au(CF3)nX4−n]− (n=4–1, X=F, CN, Cl) anions

“…Recently we have shown that the tetracyanoborate anion [B(CN) 4 ] À [13][14][15] can be converted into the tetrakis(trifluoromethyl)borate anion [B(CF 3 ) 4 ] À [16] via fluorination with ClF or ClF 3 in anhydrous HF (Eq. (9)): In contrast to CF 3 -transfer reactions employed in the synthesis of trifluoromethyl transition metal complexes so far, this approach leads to the conversion of a cyano into a CF 3 À ligand that is already attached to the central atom.…”

“…the conversion of NCCH 2 CH 2 CN to CF 3 CH 2 CH 2 CF 3 [19]. Interestingly, the reaction of organic nitriles, RCN, with ClF [20][21][22][23] or ClF 5 [24] leads in general to the formation of RCF 2 NCl 2 or RCF 2 NClF, respectively, whereas such products were not observed in the fluorination of [B(CN) 4 ] À with either ClF or ClF 3 [16].…”

Salts of novel chelatoborate anions: [R F BX(ox)] − (R F = CF 3 , C 2 F 5 ; X = F, OMe; ox = oxalato) and [R F B(OMe)(cat)] − (R F = CF 3 , C 2 F 5 ; cat = catecholato)

“…Borate anions are valuable components for materials used in many applications, for example Li + salts for battery technologies [1], ionic liquids [2,3], components of electrolytes for dyesensitized solar cells (Grä tzel cells, DSSCs [4]) [5,6], and weakly coordinating anions for the stabilization of highly reactive cations [7][8][9][10][11][12], e.g. in catalysis.…”

Conductivity, Structures, Spectra, and Thermal Properties of Lithium and Sodium Tetracyanidoborates with Crown Ether Encapsulated Cations: Isolated Ions in [AI(12‐crown‐4)2][B(CN)4] and 1D Chains in [AI (15‐crown‐5)][B(CN)4] (AI = Li, Na)

“…[4][5][6][7][8] Compounds are known that contain solvent molecules, for example, K[B(CN) 4 ]·THF [6,9] or [NH 4 ][B(CN) 4 ]·CH 3 CN, [6,9] and, furthermore, there are established tetracyanidoborate alkali cations complexed by macrocyclic polyether molecules, which show an unusual network of low-dimensional salt chains with different coordination behavior between the encapsulated alkali metal cations and the multifunctional [B(CN) 4 ]units. Therefore, tetracyanidoborates became a useful starting material for unusual anions such as [B(CF 3 ) 4 ]or [B{CN·B(C 6 F 5 ) 3 } 4 ] -, [4,[11][12][13][14][15][16][17][18][19][20] which are able to stabilize highly reactive cations. Therefore, tetracyanidoborates became a useful starting material for unusual anions such as [B(CF 3 ) 4 ]or [B{CN·B(C 6 F 5 ) 3 } 4 ] -, [4,[11][12][13][14][15][16][17][18][19][20] which are able to stabilize highly reactive cations.…”