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.