Synthesis of Aryl-Based Cyclopentadienyl Lithium Compounds for Self-Assembly and Proton Relays in Hydrazone-Based Rotary Switches

Chapter One: Synthesis of Aryl-Based Cyclopentadienyl Lithium Compounds for Self-Assembly: Cyclopentadienyl (Cp) lithium derivatives are known to form &eegr;5-coordinated, electrostatically bonded, polymeric "supersandwich" structures in the solid state, but unfortunately these compounds are not typically crystalline, which makes obtaining their solid-state properties very difficult. To overcome this problem we hypothesized that the use of CH/pi interactions could assist in the crystallization of these derivatives. Therefore, we have synthesized and characterized aryl-based CpLi compounds 1-4 in this study using NMR spectroscopy. Our hypothesis was confirmed when the benzyl-substituted CpLi 5 was observed to crystallize with CH/pi interactions which were observed to propagate throughout the crystal structure.;Chapter Two: Synthesis and Characterization of Three-Fold Symmetric 1,3,5-tris-Phenylbenzene Metallocenes: Our interest in developing aryl-based Cp ligands for self-assembly led us to develop a large, aromatic and three-fold symmetric Cp ligand based on a 1,3,5-tris-phenylbenzene (TPB) core. Three new TPB-based cyclopentadiene (CpH) compounds 2-4 were developed which include the unsubstituted ring system 2 and substituted ring derivatives on the 2,3,4,5-position to include methyl (3, CpMe) and phenyl (4, CpPh) substituents. We were able to demonstrate the coordination ability of these TPB-based Cp ligands for two of the systems. Compounds 2 and 3 were observed to react with dicobalt octacarbonyl to form the three-fold symmetric, half-sandwich cobalt carbonyl metallocenes 11 and 12..;Chapter Three: Proton Relays in Hydrazone-Based Switches: Proton relays are often observed in biological systems with their wide use found in catalysis, signaling and respiration processes. Their operation is often observed to proceed through complex pathways involving the p Ka regulation of amino acid side chains. Our recent development of hydrazone-based rotary switches has led to the discovery of a new biomimetic switching mechanism in which a zinc(II)-initiated coordination-coupled deprotonation (CCD) leads to E/Z isomerization and pK a regulations. The N-methylimidazolyl switch 3(E) was previously demonstrated to undergo a reversible, multi-step switching event through proton relay with the non-coordinating pyridine switch 1(E ). The unusual acidity of 3(Z H+) was hypothesized to be the result of allosteric and electrostatic effects, which we have now further studied and adapted into a new methylpyridine switch 4(E ). The methyl substitution on the ring caused the relative acidity of the pyridinium 4(Zn-ZH +) to increase and allowed for its use in the multi-step proton relay with 1(E). Our interest in further developing proton relay systems has led us to investigate a) the importance of H-bonding effects in these systems, b) their application using additional output mechanisms with fluorescence signaling and signal amplification events, and c) the use of a photoacid to switch hydrazones without the creation of any waste products over many cycles. These proof-of-principle processes using different switching inputs and outputs will pave the way to the development of multi-component systems which mimic their biological counterparts.