Tetrafluorenofulvalene as a sterically frustrated open-shell alkene
Bibek Prajapati1, Madan D Ambhore1, Duy-Khoi Dang2
1Wydział Chemii, Uniwersytet Wrocławski, Wrocław, Poland.
Nature Chemistry
|October 2, 2023
Summary
The study reveals tetrafluorenofulvalene (TFF) defies typical π bond rules. Its central alkene bond strengthens upon reduction to tri- and tetraanions and in the quintet state.
Area of Science:
- Organic Chemistry
- Physical Chemistry
- Materials Science
Background:
- Electronic and steric effects traditionally govern organic compound structure, characteristics, and reactivity.
- Typical π bonds weaken with oxidation, reduction, or unpairing of electrons (e.g., triplet state).
Purpose of the Study:
- To investigate the unique electronic and structural behavior of tetrafluorenofulvalene (TFF), a twisted, open-shell alkene.
- To determine if TFF adheres to established principles of π bond behavior under varying redox and spin states.
Main Methods:
- Synthesis of tetrafluorenofulvalene (TFF).
- Experimental characterization of TFF and its charged species.
- Computational analysis of TFF across seven redox states.
Main Results:
- The central alkene bond in TFF strengthens significantly in the tri- and tetraanion states.
- The triplet state of TFF exhibits a weaker alkene bond than the singlet state.
- The quintet state shows a substantially increased bond order and a flatter structure compared to the triplet state.
Conclusions:
- Tetrafluorenofulvalene (TFF) exhibits anomalous π bond behavior, challenging conventional chemical principles.
- The unique electronic structure and doubly bifurcated spin topology of TFF explain its unusual reactivity.
- Balancing effects of benzenoid aromaticity and spin pairing are key to understanding TFF's behavior.
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