Synthesis and Physicochemical Properties of Ruthenium(II) Complexes Having Pentadentate Scaffolds: Water Oxidation Activity and Deactivation Pathway. Issue 2 (29th November 2018)

• Record Type: Journal Article
• Authors: Kundu, Animesh; Khan, Srimoyee; Dey, Subhasis; Dutta, Chiranjit; Anoop, Anakuthil; Mandal, Sukanta
• Is Part Of: European journal of inorganic chemistry. Issue 2(2019)
• Page Start: 164
• Page End: 177
• Publication Date: 2018-11-29
• Subjects: Structure elucidation -- Ruthenium -- Oxidation -- Reaction mechanisms; Chemistry, Inorganic -- Periodicals; Organometallic chemistry -- Periodicals; Bioinorganic chemistry -- Periodicals; Solid state chemistry -- Periodicals; 546
• DOI: 10.1002/ejic.201801099
• Languages: English
• ISSNs: 1434-1948

Abstract

Abstract : Five mononuclear Ru II complexes supported by two pentadentate polypyridyl ligands, N, N ‐bis(2‐pyridylmethyl)‐ N ‐(bis‐2‐pyridylmethyl)amine (N4 Py) {[Ru(N4 Py)(Cl)](PF6 ), 1 Cl ; [Ru(N4 Py)(OH2 )](PF6 )2, 1 Aq } and newly designed N ‐benzyl‐ N ‐((6‐(6‐methylpyridin‐2‐yl)pyridin‐2‐yl)methyl)dipyridin‐2‐yl‐methanamine (N2 Py‐ Me Bpy‐Bz) {[Ru(N2 Py‐ Me Bpy‐Bz)(Cl)](PF6 )· MeCN, 2 Cl ·MeCN ; [Ru(N2 Py‐ Me Bpy‐Bz)(OH2 )](PF6 )2 · 3H2 O· MeOH, 2 Aq ·3H2 O·MeOH and [Ru(N2 Py‐ Me Bpy‐Bz)(MeCN)](PF6 )2 · 0.5MeCN· H2 O, 2 ACN ·0.5MeCN·H2 O } were synthesized and characterized using different spectroscopic techniques such as UV/Vis, IR, 1D and 2D NMR spectroscopy, and mass spectrometry. The physicochemical properties of complexes 1 Cl and 1 Aq, and structural analysis of 1 Aq were reported by Kojima and co‐workers ( Chem. Sci . 2012, 3, 3421–3431). Structural characterizations of 1 Cl, 2 Cl ·MeCN, and 2 ACN ·0.5MeCN·H2 O were done by using single‐crystal X‐ray diffraction analyses. Catalytic water oxidation activities of aqua‐ligated Ru II complexes, using Ce IV as sacrificial electron acceptor at pH 1, were examined. Complex 2 Aq shows higher activity as compared to 1 Aq . Electrochemical study suggests that a formal [Ru VI =O] 4+ species is the active species which triggers the oxidation of water. Mechanistic investigation reveals that O–O bond formation takes place via water nucleophilic attack (WNA) pathway. The deactivation pathway of catalyst 2 Aq has also been investigated. It was observed that complex 2 Aq lost its water oxidation activity primarily due to ligand degradation via oxidative N ‐debenzylation pathway. Abstract : Chemically driven water oxidation activities of two mononuclear Ru II ‐aqua complexes supported by pentadentate ligand scaffolds were studied. A mechanism where a formal [Ru VI =O] 4+ species acts as an active intermediate triggering O–O bond formation via water nucleophilic attack is suggested. Furthermore, an initial side reaction involving oxidative N ‐debenzylation leads to deactivation.