Date of Award

May 2019

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

Advisor(s)

Ivan Korendovych

Second Advisor

Liviu Movileanu

Subject Categories

Physical Sciences and Mathematics

Abstract

Herein described are accounts of fundamentally different projects and topics. The content of the research to be elaborated on is divided into the following 3 chapters: The focus of the first chapter, under the tutelage of Dr. Daniel Clark, details the discovery and optimization of an unusual ruthenium complex capable of enyne metathesis. The second and third chapters, under the tutelage of Dr. Ivan Korendovych, relate to the design and discovery of short peptides that self-assemble into supramolecular structures and/or provide good catalytic results. The second chapter details the design of a short dipeptide able to self-assemble and its application in the transition-metal asymmetric transfer hydrogenation (ATH) reaction of converting ketones to chiral alcohols in good yields and high enantiomeric excess. The third chapter highlights some of the unexpected observations encountered from several of our peptide designs for self-assembly including the formation of hydrogels or metallogels.

Chapter 1

Ruthenium–catalyzed enyne metathesis is a reliable and efficient method for the formation of 1,3-dienes, a common structural motif in synthetic organic chemistry. The development of new transition-metal complexes competent to catalyze enyne metathesis reactions remains an important research area. This chapter describes the use of ruthenium (IV) dihydride complexes with the general structure RuH2Cl2(PR3)2 as new catalysts for enyne metathesis. These ruthenium (IV) dihydrides have been largely unexplored as catalysts in metathesis-based transformations. The reactivity of these complexes with 1,5 through 1,7-enynes was investigated. The observed reaction products are consistent with the metathesis activity occurring through a ruthenium vinylidene intermediate.

Chapter 2

Bioinspired catalysts promote a wide range of different chemical reactions with impressive efficiencies. Nonetheless, designing bioinspired metallopeptides to catalyze chemical reactions with high enantioselectivities still remains a challenge. Self-assembly enables formation of incredibly diverse supramolecular structures with practically important functions from simple and inexpensive building blocks. Here we show how a semi-rational approach to create emerging properties can be extended to a design of highly enantioselective peptide catalysts. The designed peptides comprised of as few as two amino acid residues spontaneously self-assemble in the presence of metal ions to form supramolecular, vesicle-like nanoassemblies that promote the transfer hydrogenation of ketones in aqueous phase with excellent conversion rates and enantioselectivites (90+ % ee)

Chapter 3

As an extension of the work conducted in chapter 2 of this thesis, this third chapter will describe the observations of a few notable peptides that directly or indirectly exhibited self-assembly. Various principles of ligand design were explored during our quest to find a robust self-assembling peptide ligand capable of enantioselective catalysis. Data relating to peptide self-assembly was predominantly inferred from experimental results obtained from the ATH reactions except in cases where irrefutable microscopy images could be collected. Peptide ligands that formed interesting self-assemblies or possessed self-assembly potential include (N-tosyl)-TFF-CONH2 which, by AFM imaging showed formation of fibrils, Cp*Ir(Cl)(DPLVFF-CONH2) formed a metallogel in TFE at a 125 µM concentration, and mixing oppositely charged peptides (DP)LDFDF and (DP)LKFKF in different ratios showed improved enantioselectivity over the individually tested peptide. Excellent ATH results were also obtained with the non-assembled peptide catalyst DPLF-CONH2.

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