Luminescent halido(aryl) Pt(iv) complexes obtained via oxidative addition of iodobenzene or diaryliodonium salts to bis-cyclometalated Pt(ii) precursors

The synthesis of bis-cyclometalated halido(aryl) Pt(iv) complexes [PtX(Ar)(C<^>N)(2)], with C<^>N = cyclometalated 4-(tert-butyl)-2-phenylpyridine (bppy), 2-(p-tolyl)pyridine (tpy), 2-(2-thienyl)pyridine (thpy), or 1-phenylisoquinoline (piq), X = I, Cl, or F, and Ar = Ph (for all C<^>N ligands) or t-BuPh (for C<^>N = tpy), and the photophysical properties of the chlorido and fluorido series is reported. The oxidative addition of iodobenzene to cis-[Pt(C<^>N)(2)] precursors is demonstrated to occur in MeCN under irradiation with visible light to give complexes [PtI(Ph)(C<^>N)(2)], presumably involving radical species that also produce the activation of the solvent to give cyanomethyl complexes [PtI(CH2CN)(C<^>N)(2)]. The introduction of an aryl ligand can also be achieved by reacting cis-[Pt(C<^>N)(2)] with (Ar2I)PF6 (Ar = Ph, t-BuPh), which affords cationic intermediates of the type [Pt(Ar)(C<^>N)(2)(NCMe)](+). The subsequent addition of an iodide or chloride salt gives the corresponding iodido- or chlorido(aryl) complexes. The fluorido(aryl) derivatives can be obtained from the iodido complexes by halide exchange using AgF. The chlorido- and fluorido(aryl) complexes display intense phosphorescence in deaerated CH2Cl2 solution and poly(methyl methacrylate) (PMMA) films at 298 K from triplet excited states primarily localized on the cyclometalated ligands ((LC)-L-3) with a small MLCT admixture. Compared with the chlorido complexes, the fluorido derivatives consistently present significantly shorter emission lifetimes and higher radiative and nonradiative rate constants due to a greater MLCT contribution to the emissive state. In contrast, the introduction of the t-BuPh group did not induce significant changes in radiative rates with respect to the phenyl complexes.

Automated summary

The synthesis and photophysical properties of bis-cyclometalated halido(aryl) Pt(iv) complexes are reported. The introduction of aryl ligands through different methods and the comparison of chlorido and fluorido derivatives in terms of emission lifetimes and radiative rate constants are discussed. The study also highlights the role of radical species in the activation of solvents during the oxidative addition reaction.