Design Platform for Sustainable Catalysis with Radicals: Electrochemical Activation of Cp₂TiCl₂ for Catalysis Unveiled

Abstract

The combination of synthesis, rotating ring‐disk electrode (RRDE) and cyclic voltammetry (CV) measurements, and computational investigations with the aid of DFT methods shows how a thiourea, a squaramide, and a bissulfonamide as additives affect the EqCr equilibrium of Cp2TiCl2. We have, for the first time, provided quantitative data for the EqCr equilibrium and have determined the stoichiometry of adduct formation of [Cp2Ti(III)Cl2]−, [Cp2Ti(III)Cl] and [Cp2Ti(IV)Cl2] and the additives. By studying the structures of the complexes formed by DFT methods, we have established the Gibbs energies and enthalpies of complex formation as well as the adduct structures. The results not only demonstrate the correctness of our use of the EqCr equilibrium as predictor for sustainable catalysis. They are also a design platform for the development of novel additives in particular for enantioselective catalysis.

Diastereoselective and enantioselective photoredox pinacol coupling promoted by titanium complexes with a red-absorbing organic dye

“…Clearly, a non-linear effect is registered in our reaction. Since Ti( iii ) complexes are involved in associative or dissociative equilibria (in the case of Cp 2 TiCl 2 , the loss of the chloride ligand with the formation of the corresponding cationic complex), 26,39 the effective concentration of active titanium species can be hardly estimated. 40 Although it is difficult to attribute the suitable model to fit the data reported in Fig.…”

A Guide to Low‐Valent Titanocene Complexes as Tunable Single‐Electron Transfer Catalysts for Applications in Organic Chemistry

“…This positive effect was observed for other anions (Br − , MsO − ) as well. Cyclic voltammetric, rotating ring‐disk electrode, and DFT studies revealed that these additives are not only suitable agents to cleave the Ti−Cl bond but also form supramolecular complexes with the various titanium species in solution by coordinating to the chloride ligands [52] . In case of the [Cp 2 TiCl 2 ]/[Cp 2 TiCl 2 ] − redox couple, this formation of a precomplex leads to a shift of the redox potential to slightly more positive values.…”

“…Cyclic voltammetric, rotating ring-disk electrode, and DFT studies revealed that these additives are not only suitable agents to cleave the TiÀ Cl bond but also form supramolecular complexes with the various titanium species in solution by coordinating to the chloride ligands. [52] In case of the [Cp 2 TiCl 2 ]/ [Cp 2 TiCl 2 ] À redox couple, this formation of a precomplex leads to a shift of the redox potential to slightly more positive values. Our investigations suggested that this shift in reduction potential of the titanium(III) species may directly correlate with the observed binding affinity and abstraction power of the additive.…”

Kinetic Analysis Uncovers Hidden Autocatalysis and Inhibition Pathways in Titanium(III)-Catalyzed Ketone-Nitrile Couplings

“…Following the pioneering works on titanium­(III)-promoted and -catalyzed epoxide openings, -pinacol couplings, and -related reactions, our group has investigated catalytic-reductive Umpolung reactions in form of cross-couplings between Michael acceptors, ketones, imines, and nitriles. , More recently, we have reported titanium­(III)-catalyzed decyanations and desulfonylations . The catalytic systems of titanium­(III)-catalyzed reactions, however, are complex and additives such as amine or pyridine bases, amine hydrochlorides, and chlorotrimethylsilane have a strong effect on the reaction outcome. − Moreover, ZnCl 2 or MnCl 2 , which are formed as byproducts of the turnover-enabling catalyst reduction with Zn or Mn, have an effect on the reactions as well. As a matter of fact, a strong influence of ZnCl 2 or MnCl 2 has been observed in earlier examples of epoxide opening/radical additions to Michael acceptors, and it was concluded that these salts either led to highly coordinated transition states or acted as Lewis acid cocatalysts (Scheme ).…”