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Bawden JC, Francis PS, DiLuzio S, Hayne DJ, Doeven EH, Truong J, Alexander R, Henderson LC, Gómez DE, Massi M, Armstrong BI, Draper FA, Bernhard S, Connell TU. Reinterpreting the Fate of Iridium(III) Photocatalysts─Screening a Combinatorial Library to Explore Light-Driven Side-Reactions. J Am Chem Soc 2022; 144:11189-11202. [PMID: 35704840 DOI: 10.1021/jacs.2c02011] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Photoredox catalysts are primarily selected based on ground and excited state properties, but their activity is also intrinsically tied to the nature of their reduced (or oxidized) intermediates. Catalyst reactivity often necessitates an inherent instability, thus these intermediates represent a mechanistic turning point that affords either product formation or side-reactions. In this work, we explore the scope of a previously demonstrated side-reaction that partially saturates one pyridine ring of the ancillary ligand in heteroleptic iridium(III) complexes. Using high-throughput synthesis and screening under photochemical conditions, we identified different chemical pathways, ultimately governed by ligand composition. The ancillary ligand was the key factor that determined photochemical stability. Following photoinitiated electron transfer from a sacrificial tertiary amine, the reduced intermediate of complexes containing 1,10-phenanthroline derivatives exhibited long-term stability. In contrast, complexes containing 2,2'-bipyridines were highly susceptible to hydrogen atom transfer and ancillary ligand modification. Detailed characterization of selected complexes before and after transformation showed differing effects on the ground and excited state reduction potentials dependent on the nature of the cyclometalating ligands and excited states. The implications of catalyst stability and reactivity in chemical synthesis was demonstrated in a model photoredox reaction.
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Affiliation(s)
- Joseph C Bawden
- School of Life and Environmental Sciences, Deakin University, Geelong, Victoria 3220, Australia
| | - Paul S Francis
- School of Life and Environmental Sciences, Deakin University, Geelong, Victoria 3220, Australia
| | - Stephen DiLuzio
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States
| | - David J Hayne
- Institute for Frontier Materials, Deakin University, Geelong, Victoria 3220, Australia
| | - Egan H Doeven
- School of Life and Environmental Sciences, Deakin University, Geelong, Victoria 3220, Australia
| | - Johnny Truong
- School of Science, RMIT University, Melbourne, Victoria 3000, Australia
| | - Richard Alexander
- Centre for Regional and Rural Futures, Deakin University, Geelong, Victoria 3220, Australia
| | - Luke C Henderson
- Institute for Frontier Materials, Deakin University, Geelong, Victoria 3220, Australia
| | - Daniel E Gómez
- School of Science, RMIT University, Melbourne, Victoria 3000, Australia
| | - Massimiliano Massi
- School of Molecular and Life Sciences, Curtin University, Bentley, Western Australia 6102, Australia
| | - Blake I Armstrong
- School of Molecular and Life Sciences, Curtin University, Bentley, Western Australia 6102, Australia
| | - Felicity A Draper
- School of Life and Environmental Sciences, Deakin University, Geelong, Victoria 3220, Australia
| | - Stefan Bernhard
- Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States
| | - Timothy U Connell
- School of Life and Environmental Sciences, Deakin University, Geelong, Victoria 3220, Australia
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