Guest-Induced Assembly of Tetracarboxyl-Cavitand and Tetra(3-pyridyl)-Cavitand into a Heterodimeric Capsule via Hydrogen Bonds and CH−Halogen and/or CH−π Interaction: Control of the Orientation of the Encapsulated Guest

The guest- or solvent-induced assembly of a tetracarboxyl-cavitand 1 and a tetra(3-pyridyl)-cavitand 2 into a heterodimeric capsule 1·2 in a rim-to-rim fashion via four intermolecular CO2H···N hydrogen
bonds has been investigated both in solution and in the solid state. In the 1H NMR study, a 1:1 mixture of
1a and 2a (R = (CH2)6CH3) in CDCl3 gave a mixture of various complicated aggregates, whereas this
mixture in CDCl2CDCl2 or p-xylene-d10 exclusively produced the heterodimeric capsule 1a·2a. It was found
that an appropriate 1,4-disubstituted-benzene is a suitable guest for inducing the exclusive formation of
1a·2a in CDCl3. The ability of a guest to induce the formation of guest-encapsulating heterodimeric capsule,
guest@(1a·2a), increased in the order p-ethyltoluene < 1-ethyl-4-methoxybenzene ≤ 1-ethyl-4-iodobenzene
≤ 1,4-dibromobenzene < 1-iodo-4-methoxybenzene ≤ 1,4-dimethoxybenzene ≤ 1,4-diiodobenzene. The
1H NMR study revealed that a CH−halogen interaction between the inner protons of the methylene-bridge
rims (-O-HoutCHin-O-) of the 1a and 2a units and the halogen atoms of 1,4-dihalobenzenes and a CH−π
interaction between the methoxy protons of 1,4-dimethoxybenzene and the aromatic cavities of the 1a and
2a units play important roles in the formation of 1,4-dihalobenzene@(1a·2a) and 1,4-dimethoxybenzene@(1a·2a), respectively. A preliminary single-crystal X-ray diffraction analysis of guest@(1b·2b) (R = (CH2)2Ph; guest = 1-iodo-4-methoxybenzene or p-xylene) confirmed that the guest encapsulated in 1b·2b is
oriented with the long axis of the guest along the long axis of 1b·2b and that the iodo and the methoxy
groups of the encapsulated 1-iodo-4-methoxybenzene are specifically oriented with respect to the cavities
of the 2b and 1b units, respectively.