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Development of 2nd Row Molybdenum Dearomatization Agents

Shivokevich, Philip
Thesis/Dissertation; Online
Shivokevich, Philip
Shivokevich, Philip
Abstract Chapter 1 outlines the history of π-basic dearomatization chemistry, beginning with the introduction of the 1st generation {Os(NH3)5}2+ fragment. The requisite properties for π-basic dearomatization are identified through the development of the replacement 2nd generation {TpRe(MeIm)(CO)} system. We then follow application of the Tp ligand set to current group 6 tungsten and molybdenum dearomatization agents, and detail their ability to activate aromatic molecules. Chapter 2 outlines the synthetic procedures for access to molybdenum dearomatization. Within the discussion of these optimized conditions, we explore a range of ancillary ligand options, and discuss changes to the steric and electronic properties of the resulting molybdenum complexes. Finally, we outline the characteristics that make {TpMo(DMAP)(NO)} the preferred choice for molybdenum dearomatization chemistry. Chapter 3 explores methods to resolve the racemic molybdenum center. Here we detail a variety of strategies for enantioenrichment of our chiral molybdenum dearomatization agent. Following the resolution of the molybdenum center, we probed the ability to transfer molybdenum chirality to synthetically interesting ligands, and establish a means to determine the success of the chirality transfer. Chapter 4 illustrates an alternative synthesis to dihapto-coordination via ligand exchange. Here we report initial studies in the development of a molybdenum precursor, similar to 3rd row metal – dihapto-benzene complexes. Chapter 5 explores a dual bidentate ligand set, as a means to overcome racemization of the molybdenum center. Here we synthesized a range of complexes in an effort to mimic the steric and electronic properties of the {TpMo(L)(NO)} fragment. While we were able to produce similar electrochemical properties to molybdenum dearomatization agents, we were unable to overcome unfavorable steric interactions to produce a dihapto-coordinate complex. Chapter 6 applies the tunable hydridotris(1,2,4-triazolyl)borate (Tz) scorpionate to group 6 dearomatization chemistry. We explore the synthesis of classical scorpionate complexes, and compare their reactivity to analogous Tp complexes. We demonstrate the ability of Tz complexes to undergo reversible modulation of electronic and physical properties, which provide stabilization in highly oxidative environments. Efforts to develop a Tz – based group 6 dearomatization agent are outlined, along with preliminary results for both tungsten and molybdenum complexes.
University of Virginia, Department of Chemistry, PHD (Doctor of Philosophy), 2017
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PHD (Doctor of Philosophy)
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