Applications in crystal engineering: The designed topochemical polymerization of 1,3-butadienes and the construction of organic nanotubes.

摘要

The macroscopic properties of all materials are determined by the molecules from which it is composed and also by the relative orientation of these molecular constituents relative to one another. To rationally design materials with specific properties it is essential that the relative orientation of molecules in the solid be controlled. This is generally not possible at the current state of technology. How a molecule's structure effects and controls its packing in the solid state structure is poorly understood. The crystal structures of even the simplest organic molecules cannot be reliably predicted at the current level of technology. The use of strong directional interactions such as hydrogen bonding interactions however, has been successfully used as a strategy in constructing low dimensional solids. The true test of these designs is in their application in constructing materials with specific properties. Two goals of this group are the design of new topochemical polymerizations and the construction of porous solids.; Previous research performed in this group has demonstrated that ureylene and oxalamide functionality predictable and persistently form one-dimensional hydrogen bonded α-networks. These functionality have been used previously by this group in constructing layered solids, organizing transition metals and in organizing diacetylenes for topochemical polymerizations. The current work is concerned with using urylene and oxalamide functionality to organize molecules in the solid state for topochemical polymerizations and to construct organic nanotubes.; The topochemical reaction of interest is that of 1,3-butadienes. When 1,3-butadienes are irradiated in the solid state they may undergo [2+2] cycloadditions or 1,4-addition polymerization with neighboring molecules. In order to control the reaction it is essential to bring desired reactive centers into close contact while isolating reactive centers that would lead to unwanted products. A general strategy for designing topochemical polymerizations has been developed by this group. The strategy involves constraining monomers within layers in the crystal using one and two-dimensional hydrogen-bonded networks. The hydrogen-bonded networks act as a scaffold on which the reaction occurs. The periodicity of the hydrogen-bonded network is chosen so that it matches the molecular repeat length of the desired polymer. The polymer-network match should bring desired reactive centers into close contact and allow for a smooth transition from monomer crystal to polymer crystal. When this strategy is applied to polyisoprene, ureylene and oxalamide networks were found to match the molecular repeat for polyisoprene ($\sim$4.9Å). The periodicity of urylene and oxalamide α-networks are $\sim$4.7Å and $\sim$5.1Å. A series of 2-substituted 1,3-butadienes containing ureylene and oxalamide functionality have been synthesized and their topochemical behavior investigated. Substitution at the 2-position of the butadienes is anticipated to reduce lattice strain during reaction by allowing rotation about the butadiene monomers ‘center of gravity’ during polymerization.; The use of ureylene and oxalamide functionality to organize diacetylene-containing macrocycles has also been attempted. The use of ureylene and oxalamide functionality to organize the macrocycles should result in the formation of tubular structures. The ureylene and oxalamide functionality were chosen since they have been shown to be able to organize diacetylenes for topochemical polymerizations. If these hydrogen-bonding functionality's successfully stacked the macrocycles and organized diacetylenes for polymerization a polydiacetylene-reinforced nanotube would be produced. While this goal was not attained, significant progress has been made.