Designing Ru Catalysts for Selective C-H Bond Oxidation Reactions

Abstract

Typically, C-H bond oxidation proceeds via formation of high-valent metal oxo species. Attaining a high oxidation state of the metal complex is critical as it is the key step for many catalytic processes. Understanding ligand effects on structural and electronic changes of the metal complexes towards designing more robust catalysts is an effort of this dissertation. It will highlight initial attempts at developing novel ruthenium (Ru) catalysts and an analysis of their structural, electrochemical and spectroscopic properties. The catalytic behavior of the resulting complexes towards C-H bond hydroxylation reaction will also be shown. Chapter I introduces the background of C-H bond activation and hydroxylation reactions by Ru catalysts. Also, this chapter details the study of C-H bond hydroxylation mechanisms, reaction intermediates, the importance of C-H bond hydroxylation, electronic effects of ligands, and the pioneering work in this field. Chapter II describes development a of new Ru complex containing the pyridine alkoxide ligand, of general formula [Ru(tpy)(pyalk)Cl] (tpy = 2,2’:6’2”-terpyridine, pyalk = 2-(2′-pyridyl)-2-propanol). This chapter outlines the detailed synthesis, structural, electrochemical and spectroscopic properties of the complex by electrochemical techniques, UV Visible spectroscopy, NMR, mass spectrometry and X-ray crystallography. In order to overcome some limitations on project 1, new ruthenium complexes [Ru(MepyPO3H)(tpy)Cl] (1, tpy = 2,2’:6’2”-terpyridine , MepyPO3H = (pyridine-2-ylmethyl)phosphonic acid) and [Ru(bpyPO3H)(bpy)Cl] (2, bpy(PO3H2) = 2,2-bipyridine-6-phosphonic acid, bpy = 2,2-bipyridine) bearing phosphonate ligands were prepared and fully characterized. Catalytic properties of the complexes have been evaluated by testing their ability to catalyze C-H bond oxidation using a variety of sacrificial oxidants.