Authors: Anna Yang
Source: IDEALS (University of Illinois Urbana-Champaign) (article, 2018-03-29)
Field: Chemistry — Organic Chemistry

Understanding reaction pathways leading to tetrahedral organic cages via alkyne metathesis Porous organic cages (POCs) have garnered great interest due to their well-defined structural porosity and solution processability that provide advantageous properties for wide ranges of applications. Recently, the feasibility of constructing various POCs via multitopic dynamic covalent chemistry (DCC) has been demonstrated. The common view of successful DCC syntheses is that they proceed reversibly, ultimately allowing “error-correction” to provide thermodynamically favored products. The current approach to synthesize molecular cages is to use structure-focused strategies along with empirical methods. However, such approaches become unreliable when applied to large and complex molecular cages. Professor Makoto Fujita pointed out that the kinetic factors play an important role in the successful self-assembly of large multicomponent molecular cages. However, very little attention has been dedicated to this important topic when considering dynamic reactions. The reversible nature of dynamic reactions will result in thermodynamically favored products only when these reactions proceed via kinetically viable pathways. Recognizing the current lack of understanding in pathway design, and understanding kinetic challenges in multitopic DCC is critical for developing reliable design strategies for complex molecular cages. \nThis dissertation illustrates how to shift our thinking from structure and thermodynamics to the effects of structural variables on reaction pathways and kinetic factors in dynamic covalent chemistry. This work includes the discovery of novel kinetically trapped tetrahedral cages synthesized via alkyne metathesis (chapter 2), an investigation of the origin of the kinetic trap (chapter 3), and the development of strategies to probe the dependence of reaction pathways on structural variables of the precursor (chapter 4). The investigation of the origin of the kinetic trapping has led to easy ways to switch “on/off” the kinetic traps in a controlled manner. Selectively removing species from the “dynamic pool” offers new synthetic strategies using DCC. Using pathway analysis combined with a “toy model” approach to kinetic simulations, the effects of change in precursor size on cage forming processes were probed to corroborate observed experimental results. By changing reaction conditions, reaction pathways could be further altered to alleviate the observed effects. This work establishes that a simple extension of precursor size provides a facile approach to construct large molecular cages. Collectively, this dissertation underlines how fundamental understanding of reaction pathways and kinetics provides insights to design-in kinetically viable pathways towards desired products. Development of these guidelines is advantageous for efficient preparation of complex porous organic cages, allowing for exploration of their interesting properties and potential applications. Alkyne ; Tetrahedron ; Metathesis ; Salt metathesis reaction ; Chemistry ; Computer science ; Crystallography ; Catalysis ; Organic chemistry ; Polymerization Supramolecular Chemistry and Complexes ; Chemical Synthesis and Analysis ; Synthetic Organic Chemistry Methods