Electron in a cube: Synthesis and characterization of perfluorocubane as an electron acceptor

Abstract

Fluorinated analogs of polyhedral hydrocarbons have been predicted to localize an electron within their cages upon reduction. Here, we report the synthesis and characterization of perfluorocubane, a stable polyhedral fluorocarbon. The key to the successful synthesis was the efficient introduction of multiple fluorine atoms to cubane by liquid-phase reaction with fluorine gas. The solid-state structure of perfluorocubane was confirmed using x-ray crystallography, and its electron-accepting character was corroborated electrochemically and spectroscopically. The radical anion of perfluorocubane was examined by matrix-isolation electron spin resonance spectroscopy, which revealed that the unpaired electron accepted by perfluorocubane is located predominantly inside the cage.

The Perfluoro Cage Effect: A Search for Electron-Encapsulating Molecules

“…Polyfluorination and perfluorination typically affect organic molecules in a profound manner. − One such influence is the so-called perfluoro effect, observed for planar conjugated molecules, in which the fluorines exert a much stronger stabilizing influence on the σ molecular orbitals than on the π molecular orbitals. − Perfluorinated polyhedral organic molecules have been theoretically examined and a key prediction is a low-energy, totally symmetric LUMO derived from the overlapping inward-pointing lobes of the C–F σ* orbitals. , The molecules thus exhibit a significant electron affinity (EA), accommodating the electron largely within central cavity of the polyhedra. This prediction has now been experimentally realized in the form of the perfluorocubane anion radical with O h symmetry . Herein, we have used density functional theory (DFT) to explore both the generality and limitations of the electron-encapsulating effect across a wide range of organofluorine cages.…”

“…This prediction has now been experimentally realized in the form of the perfluorocubane anion radical with O h symmetry. 10 Herein, we have used density functional theory (DFT) to explore both the generality and limitations of the electron-encapsulating effect across a wide range of organofluorine cages. The effect, hereafter referred to as the perfluoro cage effect (PCE), indeed appears to be general, with only a handful of exceptions.…”

Perfluorocubane—a tiny electron guzzler

“…Reduction potentials measured for perfluorocubane by cyclic voltammetry and differential pulse spectrometry confirmed its predicted electron-accepting capacity and the formation of a radical anion (1). Low-temperature matrix-isolation electron spin resonance spectroscopy, in combination with g-ray radiolysis, determined a rapidly rotating radical anion.…”

Chlorinated Cubane-1,4-dicarboxylic Acids

“…The expected trend in the increase of the relative strain energy as a function of attached chlorine substituents prompted us to computationally explore also the perhalogenated diacids that were intuitively expected to be the most strained members of individual series. As a side note, the hexafluorinated cubane 6F was recently synthesized (in the form of corresponding diester), 33 while 6Cl, 6Br, and 6I are hypothetical structures so far. The calculations reveal a very large amount of strain in 6F (57.52 kcal/mol) which rapidly decreases as we go down the group (23.71 kcal/mol in 6Cl).…”