Synthesis and characterization of platinum(II) complexes of 2N1O-donor ligands with a pendent indole ring

The Pt(II) complexes of 2N1O-donor ligands containing a pendent indole, 3-[N-2-pyridylmethyl-N-2-hydroxy-3,5-di(tert-butyl)benzylamino]ethylindole (Htbu-iepp), and 1-methyl-3-[N-2-pyridylmethyl-N-2-hydroxy-3,5-di(tert-butyl)benzylamino]ethylindole (Htbu-miepp) (H denotes an ionizable hydrogen), were synthesized, and the structure of [Pt(tbu-iepp)Cl] (1) was determined by X-ray analysis. Complex 1 prepared in CH3CN was revealed to have the C2 atom of the indole ring bound to Pt(II) with the Pt(II)–C2 distance of 1.981(3) Å. On the other hand, [Pt(tbu-miepp)Cl] (2) was concluded to have a phenolate coordination instead of the C2 atom of the indole ring by 1H NMR spectra. Reaction of 1 with 1 equiv. of Ce(IV) in DMF gave the corresponding one-electron oxidized species, which exhibited an ESR signal at g = 2.004 and an absorption peak at 567 nm, indicating the formation of the Pt(II)–indole-π-cation radical species. The half-life, t1/2, of the radical species at −60 °C was calculated to be 43 s (kobs = 1.6 × 10−2 s−1).

We prepared and characterized a series of Pt(II) complexes containing an indole or an N-methylindole moiety. [Pt(tbu-iepp)Cl] (1) having a 1H-indole was revealed to have the C2 atom of the indole ring bound to Pt(II) with the Pt(II)–C2 distance of 1.981(3) Å. On the other hand, [Pt(tbu-miepp)Cl] (2) having an N-methylindole ring was concluded to be a phenolate complex. One-electron oxidized complex 1 was established as Pt(II)–indole-π-cation radical species by absorption and ESR spectral studies.Figure optionsDownload as PowerPoint slide