Ruthenium Complexes of 2, 2′‐Bipyridine‐6, 6′‐diphosphonate Ligands for Water Oxidation. Issue 19 (8th September 2016)

• Record Type: Journal Article
• Authors: Kamdar, Jayneil M.; Marelius, David C.; Moore, Curtis E.; Rheingold, Arnold L.; Smith, Diane K.; Grotjahn, Douglas B.
• Is Part Of: ChemCatChem. Volume 8:Issue 19(2016)
• Page Start: 3045
• Page End: 3049
• Publication Date: 2016-09-08
• Subjects: catalysis -- phosphonate -- redox chemistry -- ruthenium -- water splitting; Catalysis -- Periodicals; 541.39505
• DOI: 10.1002/cctc.201600359
• Languages: English
• ISSNs: 1867-3880

Abstract

Abstract: Two novel ruthenium complexes, [Ru(2, 2′‐bipyridine‐6, 6′‐diphosphonato)(pic)2 ] (2 ) (pic=4‐picoline) and [Ru(6, 6′‐diisopropyl‐2, 2′‐bipyridine‐6, 6′‐diphosphonato)(pic)2 ] (3 ) bearing phosphonate groups have been synthesized and characterized by NMR spectroscopy, elemental analyses, X‐ray crystallography, cyclic voltammetry, and UV/Vis spectroscopy. Both complexes show catalytic water oxidation activity by electrochemistry. At pH 7, the Ru II/III redox couple of2 is observed at a lower potential than that of3, yet significantly, 3 oxidizes water at a lower onset potential. At pH 1 however, 2 and3 have comparable catalytic reactivity using sacrificial oxidant Ce IV . We propose that water oxidation activities of2 and3 are influenced by overall charges. For example, in oxidizing from Ru II to Ru III at pH 7, 2 acquires a −1 overall charge whereas3 acquires a +1 charge. Charge‐dictated electrostatic effects may govern binding of a water molecule to the metal site. Abstract : Taking charge with phosphonates : The synthesis and catalysis‐relevant chemical properties of the first water oxidation complexes deliberately bearing phosphonate groups positioned to serve as metal‐bound ligands are described. The pH‐switchable properties of phosphonates afford the opportunity to study the effect of charge on catalytic activity. Charge states of P−OH/P−OR groups have a significant influence on redox and catalytic properties.