Innocent Deelectronation Chemistry - From the unified redox scale valid in all solvents to innocent deelectronation chemistry in innocent solvents

Project Information

InnoChem

Grant agreement ID: 101052935

DOI

10.3030/101052935

EC signature date 3 June 2022

Start date 1 October 2022

End date 30 September 2027

Funded under

• European Research Council (ERC)

Total cost

€ 2 498 750,00

EU contribution

€ 2 498 750,00

Coordinated by

ALBERT-LUDWIGS-UNIVERSITAET FREIBURG
Germany

Periodic Reporting for period 1 - InnoChem (Innocent Deelectronation Chemistry - From the unified redox scale valid in all solvents to innocent deelectronation chemistry in innocent solvents)

Reporting period: 2022-10-01 to 2025-03-31

Summary of the context and overall objectives of the project

InnoChem targets a unifying redox potential scale that is valid for all media. Redox potentials, and thus also pH values, are intrinsically important thermodynamic parameters within chemistry and are used to describe and predict electron and proton transfer reactions, two of the most important reaction types in chemistry; in fact, these two quantities are also of some importance outside the chemical sciences. So far, with the help of so-called extra-thermodynamic assumptions, only vague connections between redox scales exist, which are solely valid for one medium or solvent (e.g. water). InnoChem aims to lay the thermodynamic basis that justifies this unification. Based on this, data from different scales only valid for one medium will be incorporated into this scale.
Substances that do nothing more than remove an electron from a substrate without undergoing further reactions we call deelectronators (deelectronation is thus a partial step of oxidation). Although extremely useful, such compounds are surprisingly underrepresented in the chemist´s toolbox. InnoChem aims to change this by synthesizing, characterizing and testing new and very potent deelectronators. The potential of these compounds will be incorporated into the unifying scale accordingly.
Deelectronators are an essential prerequisite for creating and maintaining highly inert chemical environments in which even extremely reactive compounds remain stable, i.e. do not undergo any reaction. Utilizing this so-called pseudo gas-phase, note that this is a condensed phase, InnoChem aims to produce new reactive cations that are either not yet known or only known in the real gas phase (and partially at very low temperatures). However, the pseudo gas-phase also requires sufficiently inert solvents, which are also being investigated with InnoChem.
The reactive cations created, e.g. carbocations, are tested for their ability to be used as redox mediators for electrosynthetic or electrocatalytic reactions. This makes InnoChem relevant not only from a theoretical and academic point of view, but also from a practical one.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

With our ILSB set-up (see Figure) we determined Gibbs transfer energies of single ions with an extra-thermodynamic assumption. Our data (for the silver ion and the chloride ion) show an unexpected, and exceptional high agreement with data obtained with a different assumption determined some decades ago. This means that two different assumptions confirm each other with unprecedented accuracy. Although this is not a thermodynamically stringent correlation, it is a strong indication that both assumptions are justified. A coincidental agreement is possible, but extremely improbable. We will investigate this aspect further in the ongoing InnoChem project.
We led the basis for incorporating literature data into the unifying redox scale by measured data for the Gibbs transfer energy of the ferrocenium cation Fc+, which is still used as reference system for a many of work groups all over the world.
Through extensive research into the physicochemical properties of fluorinated benzene derivatives (xFBs), we have provided guidance to the scientific community on establishing pseudo gas-phase conditions. By combing different xFBs also the redox potential of redox systems become straightforwardly tuneable. In parallel, we have developed a number of different deelectronators with exceptionally high oxidation potentials. This enables us, as we have demonstrated, to synthesize a variety of uncommon and highly reactive cations.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The xFBs solvents for deelectronation reactions are a novelty that enables by combing them with weakly coordinating anions in a simple way pseudo gas-phase conditions. Thus, highly reactive cations can be synthesized straightforwardly. In those solvents high oxidation potentials can be reached due to their electrochemical stability. Also, common oxidation agents exhibit under these conditions a much higher potentials than in using in common solvents with usual counterions. The [naphthaleneF]+⋅[F{Al(ORF)3}2]− salt with its high deelectronation potential is comparable to ReF6 but much easier to handle. Its synthesis can be performed in the solid state leading to an high potential in the solid state. We expect that both the limits of what is physically possible in terms of synthesizing highly reactive substances will be pushed forward and that the number of such syntheses will increase.
The copper dinitrogen complex [(η1-N2)Cu(Al(ORF)4)] shows as rare example for a transition metal dinitrogen complex without strongly donating auxiliary ligands an unrivalled N2 stretching frequency of 2314 cm−1. This is the new benchmark for homoleptic dinitrogen complexes. Dinitrogen fixation is the first and basically important step in the nitrogen cycle. We do not rule out that these results will provide insights for this process.
The equality of Gibbs transfer energies of the Ag+ and the Cl− ion between several solvents obtained with two different extra-thermodynamic assumptions within a low accuracy is remarkably, and is unprecedented. This can be considered as mutual confirmation of both assumptions. However, this topic has to be investigated in more detail. If this turns out to be true, it will be a milestone for the thermodynamics of single ions.

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