Chemistry Final Defense – Ian Haltom

About the event

Speaker: Ian Haltom

Group: Dr. Jim Boncella

Title: Synthesis and reactivity of thorium(II) and zirconium(II) synthons featuring doubly-reduced metal-arene interactions

Abstract

Oxidation state is one of the most fundamental properties of any element in the periodic table. The available oxidation states for any element often dictates the chemistry that is characteristic of that specific element. The organometallic chemistry of thorium has historically been limited due its redox-inactive nature, as thorium is typically dominated by the Th(IV) oxidation state. This leaves a gap in the fundamental understanding of the chemistry available to thorium, especially in comparison to its nearby actinide neighbor uranium which has isolable oxidation states from U(I)-U(VI).  The closest transition metal surrogates for thorium are the group IV transition metals, particularly zirconium, which also shows limited redox transformations due to dominance of the M(IV) oxidation state.

In this work, the terphenyl amide ligand -NHAriPr6 (AriPr6 = 2,6-(2,4,6-iPr3C6H2)2C6H3) was utilized for its sterically-hindering framework in conjunction with chelating metal-arene (M-Ar) interactions to allow for the isolation of complexes isoelectronic to Th(II) and Zr(II). In these complexes, the chelating metal bound Ar ring has been doubly-reduced and has been rendered redox-noninnocent.

In this defense, a variety of chemical transformations will be shown which demonstrate the rich chemistry of these formally low-valent metal complexes, particularly their ability to cleanly reduce substrates by two electrons and form new bonds to the Th and Zr metal centers. This leads us to confidently assign these complexes as Th(II) and Zr(II) synthons, i.e. complexes that react in a similar fashion to electron-rich Th(II) and Zr(II) while containing Th(IV) and Zr(IV) metal centers bound to doubly reduced ligands. With this body of work, we have demonstrated that chelating M-Ar interactions are a useful framework to generate electron-rich complexes, especially those containing metal centers in, or isoelectronic to, oxidation states with limited exploration in the field.