C–H Activation of Fluoroarenes: Synthesis, Structure, and Luminescence Properties of Copper(I) and Gold(I) Complexes Bearing 2‑Phenylpyridine Ligands

Although
2-phenylpyridine (ppy)-type complexes have been employed
very successfully for the design of luminescent IrIII and
PtII complexes, corresponding d10-coinage metal
complexes are unknown. We report on the synthesis of the first, room-temperature-stable,
CuI ppy-type complexes, by C–H activation of 2-(2,3,4,5-tetrafluorophenyl)­pyridine
(Htfppy, 1) using [Cu­(OH)­(IDipp)] (2) (IDipp
= bis­(2,6-di-isopropylphenyl)­imidazole-2-ylidene) or by lithiation
of 1 and subsequent reaction with CuBr·SMe2 in the presence of a POP ligand (POP = bis­{2-(diphenyl­phosphanyl)­phenyl}
ether) in THF, giving [Cu­(tfppy)­(IDipp)] (3) or [Cu­(tfppy)­(POP)]
(4). The complexes thus obtained adopt distorted trigonal
and tetrahedral coordination geometries, respectively. Gold­(I) tfppy
complexes with IDipp (5) or PTol3 (6) ligands have also been prepared, showing a preference for linear
coordination environments due to the noncoordinating pyridine moiety
of the tfppy ligand. These structural differences have a profound
effect on the photophysical properties of the coinage metal ppy compounds.
The CuI tfppy complexes exhibit intense orange-red luminescence
(λmax = 610 (3), 607 (4) nm) from a 3(intraligand)­CT state in the solid state
at room temperature, with phosphorescence lifetimes of τ = 8.6
(3) and 9.5 (4) μs. In contrast, the
linear coordination leads to weak emission of the AuI complexes,
with 5 displaying simultaneous fluorescence and phosphorescence.
Surprisingly, reaction of 2 with Htfppy (1) in MeCN leads to solvent activation and to isolation of a copper
acetamide complex, [Cu­(N­(H)­C­(O)­Me)­(IDipp)] (14).