Singly Reduced Iridium Chromophores: Synthesis, Characterization, and Photochemistry

Abstract

One-electron reduced photosensitizers have been invoked as crucial intermediates in photoredox catalysis, including multiphoton excitation and electrophotocatalytic processes. However, such reduced chromophores have been less investigated, limiting mechanistic studies of their associated electron transfer processes. Here, we report a total of 11 different examples of isolable singly reduced iridium chromophores. Chemical reduction of a cyclometalated iridium complex with potassium graphite affords a 19-electron species. Structural and spectroscopic characterizations reveal a ligand-centered reduction product. The reduced chromophore absorbs a wide range of light from ultraviolet to near-infrared and exhibits photoinduced bimolecular electron transfer reactivity. These studies shed light on elusive reduced iridium chromophores in both ground and excited states, providing opportunities to investigate a commonly invoked intermediate in photoredox catalysis.

Shining Fresh Light on Complex Photoredox Mechanisms through Isolation of Intermediate Radical Anions

“…This has the potential to be a much more general strategy for the study of PRC mechanisms and only requires equipment that is widely accessible in synthetic laboratories. However, it has seldom been pursued until now. ,, It has recently been noted of PRC mechanisms that “reaction intermediates formed following the initial PET step [from PC] are seldom monitored and [...] there still remains much to discover about the supposedly ‘dark’ reactions of photocatalytic cycles” . As illustrated herein, isolated PC ·– represent ideal tools for the study of these missing steps.…”

Radical metallacyclopropene: synthesis, structure and aromaticity

“…S5†), similar to those of paramagnetic Ir complexes obtained from one-electron reduction of Ir( iii ) compounds. 11 As shown in Fig. 2, single crystal X-ray diffraction analysis revealed that complex 1 has a slightly distorted octahedral structure (bond angle of Cl1–Re1–P2 is 169.42(6)°), and the α-rhenabenzofuran ring (Re1, O1, C1–C7) of complex 1 is nearly planar, as reflected by the small mean deviation from the least-squares plane (0.0632 Å) and the angle sum of ideal 540.0° of rhenafuran unit.…”

Fused metallacyclopropenes from alkynylphenols

“…S13, ESI†), similar to those of paramagnetic Ir complexes obtained from one-electron reduction of cationic Ir( iii ) photoredox catalysts. 8 Its EPR spectrum has been recorded to confirm its paramagnetism (Fig. S22, ESI†).…”