A heteroleptic cyclometalated iridium(iii) fluorophenylpyridine complex from partial defluorohydrogenation reaction: synthesis, photophysical properties and mechanistic insights

Abstract

In this paper, a C–F bond activation reaction of a chloro-bridged iridium(III) dimer (dfppy)₂Ir(μ-Cl)₂Ir(dfppy)₂ (1) (dfppy denotes 2-(4,6-difluorophenyl)pyridyl) in the presence of sodium methoxide has been reported, leading to the formation of a heteroleptic cyclometalated iridium(III) fluorophenylpyridine complex 2. HPLC-mass analysis confirmed the release of formaldehyde in the product mixture. When sodium benzyloxide was used as the base, complex 2 was also generated with the release of a benzaldehyde derivative. Complex 2 has been fully characterized by ¹H-NMR, ¹⁹F-NMR and X-ray crystallographic methods, confirming the partial loss of one of the fluorine atoms on one of the cyclometalated phenylpyridyl ligands. Photophysical studies of complex 2 show that it has a similar absorption spectrum to that of Ir(III)(dfppy)₃. However, the emission spectrum shows a red shift maximum emission band at 478 nm due to the loss of a single fluorine atom, highlighting the critical effect of fluorine on the photoluminescence of these Ir(III) complexes. Finally, intensive mechanistic studies including HPLC-mass analysis, ¹H-NMR, and ¹⁹F-NMR studies demonstrate that the formation of complex 2 should involve a critical β-hydride elimination of Ir(III)-alkoxide intermediate and the participation of Ir-hydride and/or Ir-fluoride intermediates.