| Efficient syntheses of mechanically interlocked molecular compounds, such as catenanes and rotaxanes, are generally achieved with the aid of molecular recognition elements to first form a complex. Although the formation of complexes and supramolecular arrays are often thermodynamically controlled, the key step in the syntheses of mechanically interlocked molecules is generally kinetically controlled. The majority of the product formed is the desired product. However, once unwanted non-interlocked by-products form, they cannot be reused. Dynamic covalent chemistry has been utilized (Chapter 1) in the synthesis of catenanes and rotaxanes and is necessary for the formation of more complex interlocked molecular compounds. The formation of unwanted side-products is reversible, i.e. they can break apart to reform starting materials. Hence, the thermodynamic stability of the product, instead of the transition state, determines the efficiency of the synthesis. Synthesis of more complex interlocked molecular compounds using the dialkylammonium ion/crown ether recognition motif requires the functionalization of both the crown ether and dialkylammonium ion components. However, functionalization of the well-studied dibenzo[24]crown-8 results in symmetry-related complications in its analysis by 1H NMR spectroscopy and has led to ( Chapter 2) the necessity to employ symmetrically substituted crown ethers. Hence, the binding properties of pyridine-based crown ethers such as pyrido[24]crown-8 and dipyrido[24]crown-8, and their formyl derivatives, with various dibenzylammonium ions have been studied in solution as well as in the solid state. With a formyl derivative of dipyrido[24]crown-8 the synthesis of a more complex interlocked molecular compound has been accomplished ( Chapter 3) utilizing dynamic imine condensation/hydrolysis. This interlocked molecular compound is assembled using a bisammonium ion-containing "scaffold" that complexes to two diformyl crown ethers to form a [3]pseudorotaxane. The crown ethers are then connected to each other via a diamine linker to form a net-like structure around the central "scaffold." The net-like and the scaffold-like components are mechanically interlocked and cannot be taken apart without breaking covalent bonds. The syntheses of a [2]rotaxane, a bis[2]rotaxane, and daisy chain-like oligomers have also been achieved (Chapter 4) using a dynamic clipping methodology where dialkylammonium ions-containing molecules serve as templates for the formation of crown ethers. |
