Photocatalytic water oxidation mediated by iridium complexes

• Published in: Catalysis today Vol. 290; pp. 10 - 18
• Main Authors: Corbucci, Ilaria, Ellingwood, Kevin, Fagiolari, Lucia, Zuccaccia, Cristiano, Elisei, Fausto, Gentili, Pier Luigi, Macchioni, Alceo
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.07.2017
• Subjects: Iridium complexes; Photocatalysis; Water oxidation; Water splitting; Iridium complexes; Water splitting; Water oxidation; Photocatalysis
• ISSN: 0920-5861; 1873-4308
• DOI: 10.1016/j.cattod.2016.10.030

[Display omitted] •The photocatalytic activity of a series of iridium complexes toward water oxidation is explored.•Differential manometry allows simplified detection of O2 evolution.•KIE and 1H NMR studies disclose important aspects concerning the reaction mechanism and catalyst oxidative transformation. The results of a systematic investigation on the photocatalytic water oxidation activity of eight Ir complexes are reported. In particular, [Cp*IrLn]Xm [1, Ln=(H2O)3, X−m=(NO3−)2; 2, Ln=N-dimethylimidazolin-2-ylidene and (Cl−)2; 4, Ln=1,1′-dimethyl-3,3′-ethylene-diimidazol-2,2′- diylidene and Cl− X−=PF6−; 5, Ln=2-phenylpyridine (ppy) and NO3−; 6, Ln=2-benzoylpyridine (bzpy) and NO3−; 8, Ln=2,2′-bipyridine (bpy) and Cl−], [Ir(HEDTA)Cl]Na (3) and [Ir(ppy)2(OH2)2]OTf (7), whose water oxidation activity driven by chemical oxidants was already proved, were tested as mediators (10μM–100μM) in photocatalytic experiments exploiting [Ru(bpy)3]Cl2 (1mM) as photosensitizer and Na2S2O8 (2.5mM–30mM) as electron acceptor, at pH 5.2 and pH 8 by Na2SiF6/NaHCO3 and Na2B4O7 buffers, respectively. All complexes showed to be competent catalysts for the photolytic water oxidation. Best performances were obtained with 2 at pH 5.2, where TOF>2.5min−1, TON>80 and quantum yield>0.1. H/D kinetic isotopic effect was evaluated for 1, 2 and 8 and related to their tendency to undergo oxidative transformation as deduced by 1H NMR studies, using CH3COOH as molecular probe.