Christopher B. Larsen

Photoredox Catalysis with Metal Complexes Made from Earth‐Abundant Elements

Photoredox chemistry with metal complexes as sensitizers and catalysts frequently relies on precious elements such as ruthenium or iridium. Over the past 5 years, important progress towards the use of complexes made from earth-abundant elements in photoredox catalysis has been made. This review summarizes the advances made with photoactive CrIII , FeII , CuI , ZnII , ZrIV , Mo0 , and UVI complexes in the context of synthetic organic photoredox chemistry using visible light as an energy input. Mechanistic considerations are combined with discussions of reaction types and scopes. Perspectives for the future of the field are discussed against the background of recent significant developments of new photoactive metal complexes made from earth-abundant elements.

Luminescent Ni0 Diisocyanide Chelates as Analogues of CuI Diimine Complexes

The first two homoleptic Ni0 isocyanide complexes that exhibit photoluminescence from long-lived excited states are presented. Electrochemical studies indicate that in one of the complexes significant geometrical distortion occurs upon metal oxidation. The observation of luminescence, even though currently restricted to low temperatures, is an important proof-of-concept in the search for earth-abundant alternatives to photoactive complexes made from precious metals. The prospect of using Ni0 isocyanide complexes as luminophores, photoredox catalysts, or dyes in solar cells, is highly attractive.

Photophysics and Photoredox Catalysis of a Homoleptic Rhenium(I) Tris(diisocyanide) Complex

Herein a homoleptic rhenium(I) complex bearing three chelating diisocyanide ligands and its photophysical properties are communicated. The complex emits weakly from a high-energy triplet metal-to-ligand charge-transfer excited state with an 8 ns lifetime in deaerated CH3CN at 22 °C and is shown to act as an efficient photoredox catalyst comparable to [Ir(ppy)3] (ppy = 2-phenylpyridine) in representative test reactions.

Electron Transfer around a Molecular Corner

The distance dependence of electron transfer (ET) is commonly investigated in linear rigid rod-like compounds, but studies of molecular wires with integrated corners imposing 90° angles are very rare. By using spirobifluorene as a key bridging element and by substituting it at different positions, two isomeric series of donor-bridge-acceptor compounds with either nearly linear or angled geometries were obtained. Photoinduced ET in both series is dominated by rapid through-bond hole hopping across oligofluorene bridges over distances of up to 70 Å. Despite considerable conformational flexibility, direct through-space and through-solvent ET is negligible even in the angled series. The independence of the ET rate constant on the total number of fluorene units in the angled series is attributed to a rate-limiting tunneling step through the spirobifluorene corner. This finding is relevant for multidimensional ET systems and grids in which individual molecular wires are interlinked at 90° angles.