C2‐Symmetric Bissulfoximine‐Based Metal Complexes: Synthesis, Characterization and Their Electrocatalytic Activity in Oxygen Reduction Reaction

• Published in: Chemistry, an Asian journal Vol. 17; no. 12; pp. e202200160 - n/a
• Main Authors: Junaid, Qazi Mohammad, Kumar Singh, Devesh, Ganesan, Vellaichamy, Sabiah, Shahulhameed
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 15-06-2022
• Subjects: Chemical reduction; Chemistry; Coordination compounds; Glassy carbon; Hydrogen peroxide; Iron; Keywords: Dioxygen reduction ⋅Electrocatalyst ⋅ Sulfoximine ⋅Pincer ligand ⋅Nickel; Ligands; NMR; Nuclear magnetic resonance; Organic chemistry; Organometallic compounds; Oxygen reduction reactions; Selectivity
• ISSN: 1861-4728; 1861-471X
• DOI: 10.1002/asia.202200160

Sulfoximine‐based metal complexes have gained much interest in recent years owing to their promising properties in synthetic organic chemistry. These sulfoximines have been recently introduced in the field of organometallics. However, the coordination properties of pincer sulfoximine ligands and their metal complexes have not been reported. Here, a C2‐symmetric bissulfoximine‐based pincer ligand ((pyridine‐2,6‐diylbis(methylene))bis(azaneylylidene))bis(diphenyl‐λ6‐sulfanone), namely S‐P ligand and its metal [M(SP)2]2+ {M=Fe (SC‐1), Co (SC‐2), Ni (SC‐3), Cu (SC‐4)} complexes, were synthesized. The complexes were characterized by different spectroscopic techniques like UV‐Vis, IR, NMR, ESI‐MS, and single‐crystal XRD. Complexes SC‐1 and SC‐3 exhibited octahedral geometry irrespective of the metal center. The complexes were systematically explored for electrocatalytic oxygen reduction reaction (ORR) by immobilizing them on a glassy carbon electrode using Nafion. These complexes showed selective two‐electron catalytic reduction of O2 to H2O2 in which complex SC‐2 showed the highest selectivity (≈90%) and complex SC‐4 showed the highest onset potential (0.75 V).
The synthesis and characterisation of a C2‐symmetric bissulfoximine‐based ligand and its metal complexes [Fe(II), Co(II), Ni(II) and Cu(II)] are reported. These metal complexes showed selective 2e− electrocatalytic reduction of O2 into H2O2. The copper complex showed a high positive onset potential and half‐wave potential, and the cobalt complex showed the highest selectivity for the electrochemical H2O2 synthesis.