Condition Screening for Sustainable Catalysis in Single‐Electron Steps by Cyclic Voltammetry: Additives and Solvents

Abstract

Cyclic voltammetry‐based screening method for Cp2TiX‐catalyzed reactions is extended to the screening of solvents other than tetrahydrofuran for bulk electrolysis of the catalyst and radical arylation. It was found that CH3CN can be used as a solvent for both processes without additives. Furthermore, in tetrahydrofuran, squaramide L2 is more efficient than the previously reported supramolecular halide binder, Schreiner's thiourea L1. The results extend the usefulness of the proposed time and resource‐efficient screening method for designing catalysis reactions in single‐electron steps.

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

“…Indeed, Ti( iv ) species are characterized by the following reduction potentials: ca. −0.8 V vs. SCE for 3 in CH 2 Cl 2 ; 25 ca. −0.6 V vs. SCE for 11 in CH 2 Cl 2 , 28 a (see Fig.…”

“…1 ). 25 On these bases, we decided to use ([ n Pr-DMQA] + [BF4] − ) in photocatalytic titanium mediated processes, and herein, we illustrate the implementation of our idea in a highly diastereoselective (>20 : 1 d , l : meso ) pinacol coupling promoted by 5 mol% of the available Cp 2 TiCl 2 . Moreover, the application of a simply prepared and available chiral titanium Salen complex gave, in the presence of several aromatic aldehydes, satisfactory yields of the desired pinacol product with a complete diastereoselection in favour of the d , l ( syn ) diastereoisomer, and high enantiomeric excess (up to 92%).…”

Shining Light on TiIV Complexes: Exceptional Tools for Metallaphotoredox Catalysis

“…The bulk electrolysis of red solutions Cp 2 Ti IV Cl 2 , when performed in deoxygenated solvents, generally leads to the development of green solutions of the dimeric Cp 2 Ti III -(μ-Cl) 2 , which eventually can be cleaved by coordinating solvent molecules (e.g., CH 3 CN) giving rise to a deep-blue color. [83,85,86] The presence of molecular oxygen is often detrimental for the stability of the Ti III species: when those are exposed to O 2 , solutions tend to be swiftly bleached to the corresponding yellow Ti IV derivatives. [87] Due to the rapid chloride ion dissociation, [88] the presence of H 2 O can lead to unsuccessful pinacol coupling reactions.…”

“…In THF Cp 2 TiCl 2 shows a quasi‐reversible reduction wave at ca. ‐0.75 V vs. SCE, [ 82,83 ] while the chemical reversibility decreases in analogous Cp 2 Ti IV X 2 as the halogen X is changed from Cl to Br and I, following the decrease of the bond dissociation energies between metal center and peripheral halogen. Hence, in this perspective, the generation of reactive Ti III ‐based species is in principle most promising in the cases of Cp 2 Ti IV Br 2 and Cp 2 Ti IV I 2 .…”

Evaluation of Transition Metal Catalysts in Electrochemically Induced Aromatic Phosphonation

“…In order to determine the apparent rate constant of a particular reaction and compare the values among them for different catalysts, the reaction scheme, as a rule, is simplified (if its stages are established) and postulated. A highly attractive feature of single-electron step catalysis is that cyclic voltammetry (CV) is suited for prescreening new compounds and efficient reaction conditions [31,32]. CV can be used to characterize the redox-active compounds in solution as well as to study the properties of these compounds and the kinetics of the reactions.…”