期刊
INORGANIC CHEMISTRY FRONTIERS
卷 8, 期 13, 页码 3253-3265出版社
ROYAL SOC CHEMISTRY
DOI: 10.1039/d1qi00382h
关键词
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资金
- National Science Foundation [CHE-1846831]
- Welch Foundation [E-1887]
- Air Force Office of Scientific Research [FA9550-18-1-0247]
A series of bis-cyclometalated iridium complexes have been prepared, utilizing triazole or NHC-based cyclometalating ligands with substituted beta-diketiminate (NacNac) ancillary ligands. The results show that the new iridium complexes exhibit stronger excited-state reduction potentials, making them the most potent visible-light iridium photoreductants reported to date. These photoreductants are capable of activating challenging organohalide substrates, although with modest conversion rates.
A series of bis-cyclometalated iridium complexes were prepared which combine triazole or NHC-based cyclometalating ligands with substituted beta-diketiminate (NacNac) ancillary ligands. The HOMO is localized on the NacNac ligand and its energy and associated redox potential are determined by the NacNac substitution pattern. The effect of the cyclometalating ligand, relative to the more common 2-phenylpyridine derivatives, is to destabilize the LUMO and increase the triplet excited-state energy (E-T1). These results are supported by DFT calculations, which show HOMOs and LUMOs that are respectively localized on the NacNac and cyclometalating ligands. With this new design, we observe more negative excited-state reduction potentials, E(Ir-IV/*Ir-III), with two members of the series standing out as the most potent visible-light iridium photoreductants ever reported. Stern-Volmer quenching experiments with ketone acceptors (benzophenone and acetophenone) show that the increased thermodynamic driving force for photoinduced electron-transfer correlates with faster rates relative to fac-Ir(ppy)(3) and previous generations of NacNac-supported iridium complexes. A small selection of photoredox transformations is shown, demonstrating that these new photoreductants are capable of activating challenging organohalide substrates, albeit with modest conversion.
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