Crystalline and Soft Materials Based on Dative Boron-Nitrogen Bonds

The thesis describes the utilization of dative boron-nitrogen bond is used for the construction of new materials. In chapter 2.1, the synthesis of new organogels based on bisimidazolyl ligands and diboronate esters is described. Gels with a critical gel concentration as low as 0.02 wt% were obtained. The high tunability of the system allowed the development of a light-responsive gel by means of an azobenzene spacer. Structural characterization was performed by electron microscopy, rheology and X-ray analysis to better understand the aggregation of the polymer components. The association of imidazole and arylboronate esters is investigated with isothermal titration calorimetry and NMR titrations. It is shown that the association constant of imidazole is on average two orders of magnitude higher than the one of pyridyl analogues. In the second part of this chapter, the simultaneous utilization of boronate esters, imine bonds and dative boron-nitrogen bonds was exploited for the fabrication of a four-component organogel in one step. It is demonstrated that each reversible interaction can be addressed selectively by using an appropriate stimulus. In one case, the mechanical resistance of the gel could be significantly increased by a transesterification reaction between two catechols. The synthesis of self-complementary monomers for the formation of supramolecular polymers in solution is described in chapter 2.2. Analysis by DOSY NMR revealed the formation of large assemblies from monomers composed of two imidazolyl end groups and one boronate ester. In the last chapter, the directionality of the boron-nitrogen bond is explored through the de-sign and synthesis of two new tripyridyl ligands and their coordination to diboronate esters. The formation of crystalline polymers is studied by X-ray crystallography. For the first time, polymers composed of chains of macrocycles based on boron-nitrogen bond are observed.


Related material