Fe-MAN Challenge
Starting date: April 2022
Blind challenge start: 01.05.2022
Submission deadline: 15.09.2022
The Fe-MAN challenge for gas phase reactivity
The Fe-MAN challenge invites theoretical chemistry groups to:
- calculate reaction path energetics and/or
- calculate rate constants at 310K
of the protolysis reactions of organoferrate(II) anions, Ar3Fe− and ROFeR2− (Ar = Ph, Mes), with fluorinated alcohols ROH (R = CF3CH2, CF2HCH2) in the gas phase.
In case only the reaction path energetics are provided, then we require the structures, electronic and zero-point vibrational energies plus vibrational frequencies. An online form will be provided to upload the data.
An example for such a reaction would be the reaction of Ph3Fe− with
CF3CH2OH:
This reaction is provided as a training point. Read more about it here.
Background
In their endeavor to transform synthetic chemistry into more sustainable “green chemistry”, researchers have attempted to use Fe catalysts instead of Pd-based ones for routinely applied reactions such as cross couplings, as Fe is abundant and non toxic for both humans and the environment. However, the study of the involved organoiron species and their microscopic reactivity remains challenging, since Schlenk-type equilibria and solvation effects render the investigations of single organoiron species under well-defined conditions difficult.
The use of electrospray ionization (ESI) mass spectrometry can circumvent these issues. Organometallic ions are prepared under inert-gas conditions, transferred into the gas phase and mass-selected. Subsequently, the microscopic reactivity of the ions of interest is probed by collisional activation and/or ion-molecule reaction studies. In the latter, the ions are stored in quadrupole ion traps where they undergo reactions with a substrate gas. Kinetic measurements then yield rate constants of the reaction at hand. Computational chemistry, in turn, offers structures and energies of the involved reactants, intermediates, transition states and products. Methods of statistical rate theory convert them into theoretical rate constants, to which those from the experiments can be compared quantitatively. The interplay of experiment and theory thus elucidates the reaction mechanism and thereby the microscopic reactivity of the organometallic ion. This methodology was successfully proven for the protolysis of para-substituted trisarylzincate anions by 2,2,2-trifluoroethanol and quantitative agreement between experimental and theoretical rate constants within factors of 2 to 8 was achieved (https://doi.org/10.1021/acs.jpca.1c08964). This translates to about 4 kJ/mol deviations, or in other words chemical accuracy.
We propose Fe-MAN, which stands for “Ferrates – Microkinetic Assessment
of Numerical quantum chemistry” as a first attempt to blind challenge quantum chemical methods
in the prediction of activation barriers/rate constants in the gas phase with reference experimental
data. The reactions will consist of gas-phase protolysis of organoferrate(II) anions, Ar3Fe- and
ROFeR2−, by proton donors ROH (Ar = Ph, Mes; R = CF3CH2,
CF2HCH2). These reactions serve as model systems, in which the substrate ROH attacks
the nucleophilic carbon moiety of the organoferrate electrophilically and thus, represents the polar reactivity
pattern often encountered in the transmetalation step of cross couplings, such as the Sonogashira or Negishi reaction.
Fe-MAN addresses theoretical chemistry groups and is open for various computational approaches, from reaction pathway quantum chemical calculations, to molecular dynamics and machine learning approaches. The set of reactions to compute will be unveiled on the 01.05.2022. The experimental data will be provided by the Koszinowski group, but kept secret till the submission deadline (15.09.2022). Following the deadline, a joint publication will be prepared featuring all participants with valid entries.
Feel free to contact us if you have questions about the planned blind challenge.