PhD defence: Charge Separation in Ligand Design - A Dianionic C3-Symmetric Scorpionate That Supports Fe(IV) and Si(II) Centers

Opposites often attract, and this principle extends to the realm of chemistry. In the world of stable chemical entities, such as crystals and molecules, maintaining electroneutrality is the norm. Electroneutrality means having an equal number of positive (protons) and negative (electrons) charges. However, when this balance is disrupted, it results in a phenomenon known as charge separation (CS). CS gives rise to electric fields that can influence the movement of bonding electrons, thereby altering a molecule's chemical and electronic properties. This opens the door to fine control over reactivity, which is a crucial aspect for the development of greener and more waste-effective chemical processes.

While CS is a common occurrence in nature, its potential for controlling reactivity in synthetic systems remains largely underexplored and untapped. The goal of this research is to fill this gap by introducing a chemical system that inherently exhibits charge separation: tris-skatylmethylphosphonium (TSMP(2–)). This study investigates the reactivity of TSMP(2–) in the context of coordination and main-group chemistry.

This research demonstrates that TSMP(2–) can effectively and indefinitely stabilize a high-valent Fe(IV) centre. This allows for the mimicry of highly-specific and waste-effective biochemical transformations. We use a variety of spectroscopic and computational methods to explore the electronic structure of this high-valent species. Furthermore, when combined with a silicon precursor, TSMP(2–) leads to a silane with rather unusual behavior of a Si–H bond, which is thousand times more acidic than the O–H bond in benzoic acid.

We further delve into the origins of this acidity, and link it to CS as well as the unusual interatomic angles that lead to strain. Such fine and, at the same time, drastic manipulation of bond properties opens new avenues towards cheap and sustainable chemical processes.