Molecular Insights into the Ligand‐Based Six‐Proton‐ and Six‐Electron‐Transfer Processes Between Tris‐ortho‐Phenylenediamines and Tris‐ortho‐Benzoquinodiimines

This is the authors' abstract. We don't add key points for this paper.

The global demand for energy and the concerns over climate issues renders the development of alternative renewable energy sources such as hydrogen (H2) important. A high‐spin (hs) FeII complex with o‐phenylenediamine (opda) ligands, [FeII(opda)3]2+ (hs‐[6R]2+), was reported showing photochemical H2 evolution. In addition, a low‐spin (ls) [FeII(bqdi)3]2+ (bqdi: o‐benzoquinodiimine) (ls‐[0R]2+) formation by O2 oxidation of hs‐[6R]2+, accompanied by ligand‐based six‐proton and six‐electron transfer, revealed the potential of the complex with redox‐active ligands as a novel multiple‐proton and ‐electron storage material, albeit that the mechanism has not yet been understood. This paper reports that the oxidized ls‐[0R][PF6]2 can be reduced by hydrazine giving ls‐[FeII(opda)(bqdi)2][PF6]2 (ls‐[2R][PF6]2) and ls‐[FeII(opda)2(bqdi)][PF6]2 (ls‐[4R][PF6]2) with localized ligand‐based proton‐coupled mixed‐valence (LPMV) states. The first isolation and characterization of the key intermediates with LPMV states offer unprecedented molecular insights into the design of photoresponsive molecule‐based hydrogen‐storage materials.