Formation of hypervalent complexes of trifluorosilanes with pyridine and with 4-methoxypyridine, through intermolecular silicon...nitrogen interactions

Herein we report that trifluorohexylsilane (2), trifluorophenylsilane (3) and trifluoro(pentafluorophenyl)silane (4) form new hypervalent complexes with pyridine (py) and with 4-methoxypyridine (MeO-py), through intermolecular Si...N interactions. In general, stronger and more efficient binding is observed for the more electron poor (Si atom in) silane 4 and for the more electron rich (N atom in) 4-methoxypyridine. Binding constants of 15+/-2, 25+/-5, and 550+/-100 M(-1) at 25 degrees C in benzene were measured for the formation of the pentacoordinate 2.py, 3.py, and 3.MeO-py complexes, respectively. In addition, silane 3 also forms the hexacoordinate 3-2py and 3-2MeO-py complexes at low temperatures and silane 4 forms the 4-2py complex below room temperature and the 4-2MeO-py complex already at room temperature and in a high concentration. The various types of hypervalent complexes and different binding strengths described here for silanes 2-4 and previously for trifluoro(phenylethynyl)silane (1) and the possibility to modulate the binding modes (penta- vs hexacoordination) of these complexes (by the type of amine used, concentration, and the temperature applied) suggest that such new intermolecular Si...N interactions could be used as efficient and versatile binding motifs in supramolecular chemistry.