Ferrocene Acidity and C-H Bond Dissociation Energy via Experiment and Theory #

Brent Speetzen, Steven R. Kass

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The gas-phase acidity of ferrocene (Î"H°acid(1) = 391.5 ± 1.3 kcal mol-1) and electron affinity of the ferrocenyl radical (EA(1r) = 1.74 ± 0.08 eV) were measured in a Fourier transform mass spectrometer and combined in a thermodynamic cycle with the known ionization energy of the hydrogen atom to afford the C-H bond dissociation energy of 1 (BDE(1) = 118.0 ± 2.3 kcal mol-1). Companion M06-2X but not B3LYP computations reproduce each of these thermodynamic quantities and are in accord with an unusually strong aromatic C-H BDE. Natural population analysis and atomic polar tensor charges indicate that a covalent description of ferrocene with a neutral iron atom is a better representation of this compound than an ionic one with a doubly charged Fe2+ center. Predicted structural differences upon deprotonation of MCp2, M = Fe and Mg, are also in accord with this view.

Original languageEnglish (US)
Pages (from-to)6016-6021
Number of pages6
JournalJournal of Physical Chemistry A
Issue number28
StatePublished - Jul 18 2019

Bibliographical note

Funding Information:
Generous support from the National Science Foundation (CHE-1665392) and the Minnesota Supercomputer Institute for Advanced Computational Research is gratefully acknowledged.

Publisher Copyright:
© 2019 American Chemical Society.


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