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

In 2,6-diarylphenylSiR₂ 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 π-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 π-face.