Catalytic Iridium Oxide Nanoparticles

Particle Formation during Oxidation Catalysis with Cp* Iridium complexes

Hintermair, U., Hashmi, S.M., Elimelech,M., and Crabtree, R.H.

DOI Link

Real-time monitoring of light scattering and UV–vis profiles of four different Cp*IrIII precursors under various conditions give insight into nanoparticle formation during oxidation catalysis with NaIO4 as primary oxidant. Complexes bearing chelate ligands such as 2,2′-bipyridine, 2-phenylpyridine, or 2-(2′-pyridyl)-2-propanolate were found to be highly resistant toward particle formation, and oxidation catalysis with these compounds is thus believed to be molecular in nature under our conditions. Even with the less stable hydroxo/aqua complex [Cp*2Ir2(μ-OH)3]OH, nanoparticle formation strongly depended on the exact conditions and elapsed time. Test experiments on the isolated particles and comparison of UV-vis data with light scattering profiles revealed that the formation of a deep purple-blue color (∼580 nm) is not indicative of particle formation during oxidation catalysis with molecular iridium precursors as suggested previously.

The use of in-situ light scattering to monitor the formation (or lack thereof) of iridium oxide nanoparticles during catalyzed water-oxidation reactions helped to resolve a key debate in the field.  As of August 2015, this paper from 2012 has been cited nearly 70 times.  Ulrich Hintermair is now the Whorrod Research Fellow at the Center for Sustainable Chemical Technologies at the University of Bath.

View subsequent Related Work on this topic, with additional light-scattering results:

Electrochemical Activation of Cp* Iridium Complexes for Electrode-Driven Water-Oxidation Catalysis, by Thomsen, Sheehan, Hashmi, Campos, Hintermair, Crabtree, and Brudvig. Journal of the American Chemical Society 136 13826-13834 (2014).

Cp* Iridium Precatalysts for Selective C-H Oxidation with Sodium Periodate as the Terminal Oxidant, by Zhou, Hintermair, Hashiguchi, Parent, Hashmi, Elimelech, Periana, Bridvig, and Crabtree. Organometallics 32, 957–965 (2013).  

Probing the Viability of Oxo-Coupling Pathways in Iridium-Catalyzed Oxygen Evolution, by Graeupner, Hintermair, Huang, Thomsen, Takase, Campus, Hashmi, Elimelech, Brudvig, and Crabtree. Organometallics 32, 5384–5390 (2013).