Issue 8, 2020

Novel iridium complexes with N-heterocyclic dicarbene ligands in light-driven water oxidation catalysis: photon management, ligand effect and catalyst evolution

Abstract

Iridium complexes [IrClCp*diNHC]PF6, with N-heterocyclic dicarbene (diNHC) and pentamethylcyclopentadienyl (Cp*) ligands, have been investigated in light driven water oxidation catalysis within the Ru(bpy)32+/S2O82− cycle (bpy = 2,2′-bipyridine). In particular, the effect of different diNHC ligands was evaluated by employing the complex 1a (diNHC = 1,1′-dimethyl-3,3′-ethylenediimidazol-2,2′-diylidene) and the novel and structurally characterised 2 (diNHC = 1,1'-dimethyl-3,3′-ethylene-5,5′-dibromodiimidazol-2,2′-diylidene) and 3 (diNHC = 1,1′-dimethyl-3,3'-ethylene-dibenzimidazol-2,2′-diylidene). The presented results include: (i) a photon management analysis of the 1a/Ru(bpy)32+/S2O82− system, revealing two regimes of O2 evolution rate, being dependent on the light intensity at low photon flux, where the system reaches an overall quantum yield up to 0.17 ± 0.01 (quantum efficiency 34 ± 2%), while being independent of light intensity at high photon flux thus indicating a change of limiting step; (ii) a trend of O2 evolution activity that follows the order 1a > 2 > 3 both under low and high photon flux conditions, with the reactivity that is favoured by the electron donating nature of the diNHC ligand, quantified on the basis of the carbene carbon chemical shift; (iii) an analogous trend also in the bimolecular rate constants of electron transfer kET from the iridium species to photogenerated Ru(bpy)33+, with kET values in the range 4.2–6.1 × 104 M−1 s−1, thus implying a significant reorganisation energy to the iridium sphere; (iv) the evolution of 1a, as the most active Ir species in the series, to mononuclear iridium species with lower molecular weight and originating from oxidative transformation of the organic ligand scaffold, as proven by converging UV-Vis, MALDI-MS and 1H-NMR evidences. These results can be used for the further design and engineering of novel catalysts.

Graphical abstract: Novel iridium complexes with N-heterocyclic dicarbene ligands in light-driven water oxidation catalysis: photon management, ligand effect and catalyst evolution

Supplementary files

Article information

Article type
Paper
Submitted
20 דצמ 2019
Accepted
04 פבר 2020
First published
05 פבר 2020

Dalton Trans., 2020,49, 2696-2705

Novel iridium complexes with N-heterocyclic dicarbene ligands in light-driven water oxidation catalysis: photon management, ligand effect and catalyst evolution

A. Volpe, M. Natali, C. Graiff, A. Sartorel, C. Tubaro and M. Bonchio, Dalton Trans., 2020, 49, 2696 DOI: 10.1039/C9DT04841C

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements