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

Abstract

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).