Mono(arylhydrazino)acenaphthenones as a platform for the design of NIR chromophores based on Pd(ii)-BIAN complexes

Abstract

A new synthetic procedure for mono(arylhydrazino)acenaphthenones Ph-mhan (1) and 2-tol-mhan (2), based on the reaction of acenaphthenequinone with an arylhydrazonium salt, has been developed. These compounds were used further to obtain a series of heteroleptic cationic palladium(II) complexes containing bis(arylimino)acenaphthene (Ar-bian) and mono(arylhydrazino)acenaphthenone (Ar-mhan) ligands: [Pd(tmp-bian)(Ph-mhan)](CF₃SO₃)₂ (3), [Pd(tmp-bian)(2-tol-mhan)](CF₃SO₃)₂, (4), and [Pd(dpp-bian)(Ph-mhan)](CF₃SO₃)₂ (5). The resulting compounds were characterized by X-ray diffraction analysis, ¹H NMR, IR and UV spectroscopy, cyclic voltammetry, and quantum chemical calculations. All complexes show a reversible reduction at −0.31 to −0.41 V (vs. Ag/AgCl) localized on the Ar-bian ligand, followed by an irreversible reduction at −1.27 to −1.46 V (vs. Ag/AgCl) of the Ar-mhan moiety. Electronic absorption spectra of 3–5 reveal a characteristic band in the near-IR region (∼700 nm), corresponding to the intramolecular ligand-to-ligand charge transfer (LL′CT) from Ar-mhan (π-donor) to Ar-bian (π-acceptor).