N,N,O Pincer Ligand with a Deprotonatable Site That Promotes Redox‐Leveling, High Mn Oxidation States, and a Mn₂O₂ Dimer Competent for Catalytic Oxygen Evolution

Abstract

The new complex [Mn(bipyalk)(H2O)(µ‐O)]2(OTf)2 {bipyalk = 2‐([2,2′‐bipyridin]‐6‐yl)propan‐2‐olate} catalyzes oxygen evolution with a TOF of 0.0055 s–1 when driven by the sacrificial oxidant KHSO5 in water. It is proposed on the basis of EPR experiments that the catalyst proceeds through a MnV(µ‐O)2MnV=O intermediate supported by the highly donating tertiary alkoxide moiety of the ligand. The Mn(IV,IV) dimer can also be formed electrochemically from its precursor, Mn(bipyalkH)Cl2. A related series of bis‐ligated monomers of the type [Mnn(bipyalkHx)(bipyalkHy)](PF6)2 is also reported, where the dication features MnII, MnIII, and MnIV oxidation states and corresponding protonation states. Electrochemical data on this series underscore the importance of proton loss at the alcohol/alkoxide moiety during oxidation to maintain low overpotentials required for catalysis.

Bio-Inspired Molecular Catalysts for Water Oxidation

“…It was proposed that O-O bond formation involved the attack of water (or oxone) on a Mn V =O intermediate. Other functional µ-oxo-bridged dinuclear models included [Mn((PaPy 3 )(µ-O)(PaPy 3 )Mn] 2+ (67), reported by Brudvig and coworkers in 2013 with a TOF of 13.9 × 10 −3 s −1 using oxone as an oxidant [141], and the recent complex, [Mn(bipyalk)(H 2 O)(µ-O) 2 Mn(bipyalk)](OTf) 2 (68), reported by Crabtree, Brudvig and coworkers that achieved a TOF of 5.5 × 10 −3 s −1 with oxone as an oxidant [142]. Additionally, three functional mononuclear manganese complexes, 69-71, were developed by Brudvig and coworkers in 2013 [141].…”

Strategic Synthesis of Heptacoordinated FeIII Bifunctional Complexes for Efficient Water Electrolysis

“…In order to eliminate the major challenges of electrocatalysis e.g., high activation energy barrier, poor catalytic durability, redox balancing, several redox processes between the metal centres, [25][26][27][28] etc., we have strategically designed these types of dinuclear catalysts taking into account the following targets: (i) excellent stability of molecular WSCs by tuning the electronic/steric properties of the ligand which requires meticulous screening depending upon its nature, (ii) arrangement of a pre-organised ligand by developing higher C R as well as multinuclear complexes to increase the electronegativity and subsequent activity of the metal centre which facilitates the H 2 O splitting, (iii) subsequent replacement of the À Cl À ions by a bridging À SO 4 2À ion for delocalization of the electron density over the molecular catalyst, and (iv) development of abundant active sites with modified electron density for favourable adsorption of H 2 O splitting intermediates.…”

Recent Progress with Pincer Transition Metal Catalysts for Sustainability

“…The process is key for the development of the hydrogen economy that requires green and sustainable hydrogen produced via solar or wind energy. Many groups explored various combinations of metals and pincer ligation [14,162,163]; in particular, several works report the use of Milstein Ru-PNP catalyst 3 for this transformation [164][165][166][167][168][169].…”