Organometallic Iridium Complex Containing a Dianionic, Tridentate, Mixed Organic–Inorganic Ligand

A pentamethylcyclopentadienyl–iridium complex containing a tricyclic, dianionic, tridentate, scorpionate (facial binding), mixed organic–inorganic ligand was synthesized and characterized by single-crystal X-ray crystallography, as well as polynuclear NMR, UV–vis, and IR spectroscopies. The central cycle of the tridentate ligand consists of a modified boroxine in which two of the boron centers are tetrahedral, anionic borates. The complex is stable to hydrolysis in aqueous solution for >9 weeks at 25 °C but reacts with a 50 mM solution of sodium periodate within 12 s to form a periodate-driven oxygen evolution catalyst that has a turnover frquency of >15 s–1. However, the catalyst is almost completely deactivated within 5 min, achieving an average turnover number of ca. 2500 molecules of oxygen per atom of iridium. Nanoparticles were not observed on this time scale but did form within 4 h of catalyst activation under these experimental conditions. The parent complex was modeled using density functional th...