Exploring ligand non-innocence of coordinatively-versatile diamidodipyrrinato cobalt complexes

Exploring the Redox Properties of Bench-Stable Uranyl(VI) Diamido-Dipyrrin Complexes

The uranyl complexes UO₂(OAc)(L) and UO₂Cl(L) of the redox-active, acyclic diamido–dipyrrin anion L^– are reported and their redox properties explored. Because of the inert nature of the complexes toward hydrolysis and oxidation, synthesis of both the ligands and complexes was conducted under ambient conditions. Voltammetric, electron paramagnetic resonance spectroscopy, and density functional theory studies show that one-electron chemical reduction by the reagent CoCp₂ leads to the formation of a dipyrrin radical for both complexes [Cp₂Co][UO₂(OAc)(L^•)] and [Cp₂Co][UO₂Cl(L^•)].

Air-stable uranyl complexes of diamido−dipyrrin ligands undergo one-electron reduction to form highly air-sensitive ligand radical complexes instead of uranyl(V) complexes seen for diimine analogues.

Enhanced Hydrogen Evolution in Neutral Water Catalyzed by a Cobalt Complex with a Softer Polypyridyl Ligand

To explore the structure-function relationships of cobalt complexes in the catalytic hydrogen evolution reaction (HER), we studied the substitution of a tertiary amine with a softer pyridine group and the inclusion of a conjugated bpy unit in a Co complex with a new pentadentate ligand, 6-[6-(1,1-di-pyridin-2-yl-ethyl)-pyridin-2-ylmethyl]-[2,2']bipyridinyl (Py3Me-Bpy). These modifications resulted in significantly improved stability and activity in both electro- and photocatalytic HER in neutral water. [Co(Py3Me-Bpy)(OH₂ )](PF₆ )₂ catalyzes the electrolytic HER at -1.3 V (vs. SHE) for 20 hours with a turnover number (TON) of 266 300, and photolytic HER for two days with a TON of 15 000 in pH 7 aqueous solutions. The softer ligand scaffold possibly provides increased stability towards the intermediate Co^I species. DFT calculations demonstrate that HER occurs through a general electron transfer/proton transfer/electron transfer/proton transfer pathway, with H₂ released from the protonation of Co^II -H species.