Charge-enhanced pyridyl trifluoroborate organocatalysts: crystal structures and reactivity

The crystal structures of eleven 3- and 4-pyridyl borate salts with a variety of cations are reported. These are potassium trifluoro(pyridin-3/4-yl)borate, K⁺·C₅H₄BF₃N^-, 1 and 2 (as the monohydrate), tetrabutylammonium trifluoro(pyridin-3/4-yl)borate, C₁₆H₃₆N⁺·C₅H₄BF₃N^-, 3 and 4, tetraphenylphosphonium trifluoro(pyridin-3/4-yl)borate, C₂₄H₂₀P⁺·C₅H₄BF₃N^-, 5 and 6, tetrakis(3,5-dimethoxyphenyl)phosphonium trifluoro(pyridin-3/4-yl)borate, C₃₂H₃₆O₈P⁺·C₅H₄BF₃N^-, 7 and 8, and tetrakis[4-(dimethylamino)phenyl]phosphonium trifluoro(pyridin-3/4-yl)borate, C₃₂H₄₀N₄P⁺·C₅H₄BF₃N^-, 9 and 10, and the hemihydrate, C₃₂H₄₀N₄P⁺·C₅H₄BF₃N^-·0.5H₂O, 10h. The effects of the position of the pyridine N atom and the identity of the cations on the crystal packing of the salts are examined. The N...H and F...H anion-cation contacts and the Hirshfeld surface compositions of the anions for the salts containing organic cations are compared to the reactivity of the salts in a low-polarity solvent to look for trends between solid-state features and solution-state reactivity.