Competition between π-Arene and Lone-Pair Halogen Coordination of Silylium Ions?

In 2,6-diarylphenylSiR(2) cations, the 2,6-diarylphenyl (m-terphenyl) scaffold blocks incoming nucleophiles and stabilizes the positive charge at silicon by lateral ring interactions. Direct ortho-halogen and pi-electron-rich face coordination to silicon has been seen. For a series of cations bearing 2,6-difluoro-2',6'-dimethyl-X(n)-substituted rings, the relative contribution of these two modes of stabilization has been assessed. Direct coordination from an aryl fluoride is found to be comparable to that from the mesityl pi-face.