Although there have been a lot of reports on the synthesis and properties of [n]rotaxanes (mainly n = 2), only a few reports on the synthesis of [1]rotaxane has been published by Vögtle's group and others (see ref 5). Generally speaking, [1]rotaxane might be expected to exhibit properties different from other rotaxanes, because the rotor and the axle in the [1]rotaxane is bound covalently and closely. We report on a novel method to make [1]rotaxanes via covalent bond formation from a macrocyclic compound. That is, we first prepared a bicyclic compound from macrocycle and then proceeded to [1]rotaxane by aminolysis. This is the first synthetic example of preparation of [1]rotaxane via covalent bond formation, not utilizing weak interactions such as hydrogen bonding, charge transfer, via metal complexation, etc. This method might provide a powerful and new tool for construction of [1]rotaxane as a new supramolecular system. In addition, we investigated energy transfer from rotor to axle using [1]rotaxane that we prepared. Energy transfer occurred perfectly from the naphthalene ring of the rotor to the anthracene ring of the axle. We found also that only lithium ion among alkali ions can drastically enhance the fluorescence intensity. This finding could be applicable to ion-sensing systems, switching devices, and so on.

The internal rotational barrier heights of phenol and anisole were calculated using several basis sets up to cc-pVQZ with MP2-level electron correlation correction to evaluate the basis set effects. The calculations showed that the effects of the further improvement of the basis set beyond the cc-pVTZ were very small. Although the electron correlation substantially increased the barrier heights of the two molecules, the effects of the electron correlation beyond the MP2 method were not large. The barrier heights calculated with the CCSD(T) method were close to those with the MP2 method. The internal rotational potentials of methoxy and hydroxyl groups of o-hydroxyanisole were calculated at the MP2/cc-pVTZ//HF/6-311G** level. The calculated potentials were compared with those of phenol and anisole. o-Hydroxyanisole preferred planar structure in which the hydroxyl group had an intramolecular hydrogen bond with the oxygen atom of the methoxy group. The calculated torsional potential of the methoxy group had the maximum (7.30 kcal/mol) when the methoxy group rotated 180° from the minimum energy structure, in which the hydroxyl group did not have the hydrogen bond. The barrier height of the methoxy group of o-hydroxyanisole was considerably larger than that of anisole (2.99 kcal/mol). The large internal rotational barrier height of o-hydroxyanisole showed that the intramolecular hydrogen bond greatly stabilized the energy minimum structure and that the hydrogen bond strictly restricted the conformational flexibility of the methoxy group.

No abstract

The structure of a tetra-coordinated zinc(II) complex with a salen ligand was determined for the first time; unexpectedly, the complex was an interesting 2:2 metal-to-ligand complex.