Irradiation of Cp2TiCl2 with green light leads to electronically excited [Cp2TiCl2]*. This complex constitutes an efficient photoredox catalyst for the reduction of epoxides and for 5‐exo cyclizations of suitably unsaturated epoxides. To the best of our knowledge, our system is the first example of a molecular titanium photoredox catalyst.

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.

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.

Irradiation of Cp 2 TiCl 2 with green light leads to electronically excited [Cp 2 TiCl 2 ]*. This complex constitutes an efficient photoredox catalyst for the reduction of epoxides and for 5-exo cyclizations of suitably unsaturated epoxides. To the best of our knowledge, our system is the first example of a molecular titanium photoredox catalyst.

Low-valent titanocene catalysts are a versatile tool for organic synthesis. They promote inter-and intramolecular reactions ranging from homolytic bond cleavages to reductive umpolung reactions to additions and cyclizations in single electron steps. These reactions heavily depend on the redox potential of an in situ formed titanium(III) center, which can be adjusted by the choice of appropriate ligands. We herein review various chiral and achiral ligand-modified titanocene catalysts and their reduction potentials E p/2 obtained via cyclic voltammetry. The latter are found to correlate with the Hammett parameters σ p of the cyclopentadienyl substituents and to the pK a values of the corresponding acids of the TiÀ X ligands. For selected examples, we further discuss how the adjustment of the redox properties through modifications of the titanocene ligands can lead to greatly improved reaction outcomes in titanium(III) catalyzed single-electron transfer reactions.

What mechanism‐based screening for titanocene catalysis is all about! Combining the methods of computational chemistry and electrochemistry provides the structural and quantitative means for an efficient optimization of reaction conditions in the H‐bond donor‐assisted, titanocene‐catalyzed radical arylation of epoxides. These methods give an answer to how and why condition screening in titanocene catalysis works! More information can be found in the Full Paper by A. Gansäuer et al. on page 4903.