Identification of Ti(salen) Complexes for Efficient Catalysis in Single‐Electron Steps by Cyclic Voltammetry

TL;DR

Researchers identified a highly active Ti(salen) catalyst for a chemical reaction using electrochemical methods and calculations, without performing actual reactions.

Contribution

A new Ti(salen) catalyst was identified using cyclic voltammetry and DFT, avoiding direct catalytic testing.

Findings

The most active catalyst has a tetrasubstituted ligand backbone that prevents chloride binding.

The catalyst works efficiently in ethyl acetate with base metals or electrochemical activation.

The Ti(salen) catalyst outperforms titanocene in sustainability and substrate scope.

Abstract

We describe the identification of an active Ti(salen) catalyst for the radical arylation of epoxides by a cyclic voltammetry study of mechanism‐based predictors, such as the redox potentials of the complexes and their EqCr‐equilibria, for the success of catalysis. Surprisingly, by far the most active catalyst features an uncommon tetrasubstituted ligand backbone, which renders chloride binding to the active Ti(III) species less favorable, thereby increasing catalyst activity due to improved substrate binding. Catalysis is most efficient in the “green” solvent ethyl acetate and can be initiated using base metals as well as electrochemical methods for the reduction of the Ti(salen)‐precatalyst. Compared to the commonly employed titanocene catalysis, the use of the newly developed Ti(salen) catalyst allows for the use of milder and more sustainable reactions conditions, a broader substrate scope, and facile modification of the catalyst's electronic and steric properties.

Catalyst screening without catalysis. By combining cyclic voltammetry and DFT calculations we were able to identify a highly active catalyst for the radical arylation of epoxides without performing any reactions. The prevention of chloride binding that leads to catalyst inhibition was established as the key structural feature. Our best catalyst is applicable for a broad variety of substrates after electrochemical or chemical activation.

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