Molybdenum Quinonoid Complexes: Synthesis, Characterization, and Reactivity

Author: Henthorn, Justin Travis

Year: 2016

Degree: Dissertation (Ph.D.)

Advisor: Agapie, Theodor

Committee Members: Peters, Jonas C.; Agapie, Theodor; Stoltz, Brian M.; Gray, Harry B.

Option: Chemistry

DOI: 10.7907/Z9V40S53

Abstract

Pi-bound Molybdenum-quinonoid complexes supported by pendant phosphines were prepared and investigated for metal-ligand cooperative reactivity and access to multiple equivalents of protons and electrons within a single transition metal complex. Chapters 3, 4, and 5 of this dissertation describe the synthesis, characterization, and reactivity of these complexes in the context of multiproton, multielectron chemistry and small molecule activation.

Chapter 2 presents the synthesis of an unprecedented bis-borane supported peroxide dianion, prepared from a mixture of ferrocenes, borane, and dioxygen. The peculiarity of such a structure is emphasized, and reactivity explored. While ferrocenes of varying reduction potential were found to lead to the peroxide, only tris(pentafluorophenyl)borane was found to yield isolable peroxide, with other boranes leading to oxygenation or borate formation.

Chapter 3 describes the synthesis of a series of π-bound Molybdenum-quinonoid complexes and explores their reactivity with dioxygen. The Mo-quinonoid interaction is probed and elucidated through a number of reactions and experiments, highlighting the importance of the electronic coupling of the metal center with the organic fragment on overall reactivity with O2.

Chapter 4 further explores the π-bound Molybdenum-quinonoid complexes in various protonation and oxidation states, totaling four electrons and two protons accessible to the system. Proton-coupled electron transfer was demonstrated in two different oxidation states, and the effects of the metal-quinonoid interaction on the transfer of protons and electrons investigated thermochemically.

Chapter 5 explores the potential for π-bound Molybdenum-quinonoid complexes to access inner-sphere reactivity. The activation of E–X bonds, including H2 and PhSiH3, is demonstrated, as well as catalytic hydrosilylation of aldehydes.

Appendix A describes initial investigations into the preparation of heterobimetallic complexes supported by the catechol-diphosphine ligand framework. The synthesis of heterobimetallic MoCu complexes is presented and their structural parameters discussed.

Appendix B outlines the synthesis of multinucleating ligand platforms based off bipyridine frameworks, for the preparation of biologically inspired multimetallic complexes. Dioxygen reactivity of a dicopper system is also briefly presented.

Appendix C contains relevant NMR spectra for the compounds presented in the preceding sections.

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