Quantitative Self-Assembly of [2]Catenanes and Cages Possessing Transition Metals in Their Backbones

This thesis describes highly efficient self-assembly of various catenanes and nano-sized cage-like structures by incorporating transition metal centers into their backbones. Catenanes are very curious compounds, named after Latin word: catena, which means a chain. As indicated by its name, two or more ring-compounds interlock each other to take a chain-like structure. Following the general review of metal-directed self-assembly and general summary of the thesis. Chapter 2 describes the quantitative formation of catenane compounds by the complexation of Pd(II) and some pyridine-based ligands. The catenane structure, revealed by X-ray diffractions, indicates that the two factors, interactions between aromatic rings and the structure of monomer rings, are quite important for [2]catenane formations. If the monomer frameworks have appropriate cavity with ca. 3.5 Å surface-surface distance, the two monomers are spontaneously interlocked into [2]catenanes with aid of efficient CH-π and hydrophobic interactions. Other outstanding point is, in this chapter, the behavior as "molecular magic ring". Their strategy makes the [2]catenane structures from two pre-formed ring compounds, which can slippage into a catenane structure via transmetallation processes. This "Mobius strip" mechanism proposed here is also discussed. Labile coordinate bonds between metal centers [Pd(II)] and pyridine rings (Py) make it possible to efficiently generate the catenanes. Components, metal centers and pyridine-based ligands, in a system are led to the most thermodynamically stable situations as the results of equilibration due to this coordinate bonds [Pd(II)-Py]. The other advantage point in the utilization of coordinate bonds is that each transition metals has unique properties on a length, strength, direction, and numbers of bonds between a metal center and a organic ligand. These properties make it useful to rationally design various well-defined structures. Many examples of well-defined structures are ascribed to the geometry or coordinate bonds. Charter 3 describes a new strategy based on pure coordination chemistry for constructing a 4-crossing [2]catenane. A combination of two kinds of metal centers enabled us to obtain such a complex structure. The ligand used here contains a central 1, 10-phenanthroline site attached to two pendent/4-pyridyl groups. The central site is used to complex a copper(I) center, tetrahedral geometry, whereas the lateral pyridine groups are coordinated to palladium(II), square planar geometry. The stepwise complexation procedure is virtually quantitative. It can be carried out both ways (copper(I) followed by palladium(II) or reverse one). Interestingly, the complex is a chiral species incorporation 4 ligands, 2 copper(I) and 4 palladium(II) enters. The properties based on chirality are also mentioned. In contracts to geometries of coordination bonds, their strength should be also paid special attention. Normally, coordination bonds are classified into two parts, labile coordinate bonds and inert ones. In chapter 4, "a molecular lock" concept and its application to the synthesis of stable catenanes and square complexes. The molecular lock concept stems from the unique dual character of a Pt(II)-pyridine coordinate bond. That is, the Pt(II)-Py bond is inert under room temperature in watter. However the bond becomes labile in highly polar media at elevated temperature. Due to this behavior, the Pt(II)-Py coordinate bond can be locked and released and, hence, is likened to a lock. By the incorporation of this Pt(II)-Py bond or "molecular lock" into ring frameworks, the one-way formation of a [2]catenane is achieved. Application of molecular lock into the synthesis of kinetically stable tetranuclear square complex is also described. In chapter 5, the molecular lock concept is applied to the construction of a nano-sized cage complex. The reversibility of Pt(II)-pyridine coordinate bond can be controlled to labile bond from inert one by external stimuli. By incorporating Pt(II)-Py bond or "molecular lock" into the vicinity of cage structure, a kinetically stable nano-sized cage complex was obtained. A suitable guest molecule showed remarkable template effect for the generation of the cage compound. In addition, the assembled complex was revealed to have remarkable stability toward acidic or basic conditions