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 + ·C 5 H 4 BF 3 N − , 1 and 2 (as the monohydrate), tetrabutylammonium trifluoro(pyridin-3/4-yl)borate, C 16 H 36 N + ·C 5 H 4 BF 3 N − , 3 and 4 , tetraphenylphosphonium trifluoro(pyridin-3/4-yl)borate, C 24 H 20 P + ·C 5 H 4 BF 3 N − , 5 and 6 , tetrakis(3,5-dimethoxyphenyl)phosphonium trifluoro(pyridin-3/4-yl)borate, C 32 H 36 O 8 P + ·C 5 H 4 BF 3 N − , 7 and 8 , and tetrakis[4-(dimethylamino)phenyl]phosphonium trifluoro(pyridin-3/4-yl)borate, C 32 H 40 N 4 P + ·C 5 H 4 BF 3 N − , 9 and 10 , and the hemihydrate, C 32 H 40 N 4 P + ·C 5 H 4 BF 3 N − ·0.5H 2 O, 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.