Molecular and heterogenized dinuclear Ir-Cp* water oxidation catalysts bearing EDTA or EDTMP as bridging and anchoring ligands

Chiara Domestici, Leonardo Tensi, Francesco Zaccaria*, Nade Kissimina, Massimiliano Valentini, Roberto D'Amato, Ferdinando Costantino, Cristiano Zuccaccia, Alceo Macchioni

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

6 Citations (Scopus)

Abstract

The development of efficient water oxidation catalysts (WOCs) is of key importance in order to drive sustainable reductive processes aimed at producing renewable fuels. Herein, two novel dinuclear complexes, [(Cp*Ir)2(μ-κ3-O,N,O-H4-EDTMP)] (Ir-H4-EDTMP, H4-EDTMP4− = ethylenediamine tetra(methylene phosphonate)) and [(Cp*Ir)2(μ-κ3-O,N,O-EDTA)] (Ir-EDTA, EDTA4− = ethylenediaminetetraacetate), were synthesized and completely characterized in solution, by multinuclear and multidimensional NMR spectroscopy, and in the solid state, by single crystal X-Ray diffraction. They were supported onto rutile TiO2 nanocrystals obtaining Ir-H4-EDTMP@TiO2 and Ir-EDTA@TiO2 hybrid materials. Both molecular complexes and hybrid materials were found to be efficient catalysts for WO driven by NaIO4, providing almost quantitative yields, and TON values only limited by the amount of NaIO4 used. As for the molecular catalysts, Ir-H4-EDTMP (TOF up to 184 min−1) exhibited much higher activity than Ir-EDTA (TOF up to 19 min−1), likely owing to the higher propensity of the former to generate a coordination vacancy through the dissociation of a Ir–OP bond (2.123 Å, significantly longer than Ir–OC, 2.0913 Å), which is a necessary step to activate these saturated complexes. Ir-H4-EDTMP@TiO2 (up to 33 min−1) and Ir-EDTA@TiO2 (up to 41 min−1) hybrid materials showed similar activity that was only marginally reduced in the second and third catalytic runs carried out after having separated the supernatant, which did not show any sign of activity, instead. The observed TOF values for hybrid materials are higher than those reported for analogous systems deriving from heterogenized mononuclear complexes. This suggests that supporting dinuclear molecular precursors could be a successful strategy to obtain efficient heterogenized water oxidation catalysts.

Original languageEnglish
Pages (from-to)1614-1625
Number of pages12
JournalScience Bulletin
Volume65
Issue number19
DOIs
Publication statusPublished - Oct 15 2020

Keywords

  • Dinuclear complexes
  • Heterogenized catalysts
  • Homogeneous catalysis
  • Organometallic chemistry
  • Renewable fuels
  • Water oxidation

ASJC Scopus subject areas

  • General

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