A molecular tweezer having two bidentate pentafluorophenyl (C 6 F 5 ) groups was synthesized, and the -stacking ability of the C 6 F 5 groups toward benzene derivatives in a polar organic solvent was evaluated. The structure of the molecular tweezer was revealed to be dimeric in the crystalline state by X-ray analysis. Association constants (K a ) between the molecular tweezer and aromatic guests in THF were found to be roughly correlated with the quadrupole moment (Q zz ) of the guests, suggesting that the quadrupole-quadrupole contribution plays a significant role in the -interaction even in a polar organic solvent.

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Reaction. -The new molecular tweezers (VI) are synthesized by a slight modification of the known procedure. In the aldol reaction step, the reaction of (IIb) with (I) under conditions as for (IIa) is not successful. Thus, ketone (I) is converted to the enolate anion and then reacted with (IIb) to give (IIIb) successfully. The final step for introduction of the pentafluorophenyl groups results in a low yield of products (VI) and requires a large excess of (V) with a long reaction time. However, the modified Suzuki-Miyaura coupling reaction turns out to be applicable to dibromide (IVa) to obtain the tweezer (VIa). -(KORENAGA*, T.; KOSAKI, T.; KAWAUCHI, Y.; EMA, T.; SAKAI, T.;