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

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)](CF 3 SO 3 ) 2 ( 3 ), [Pd(tmp-bian)(2-tol-mhan)](CF 3 SO 3 ) 2 , ( 4 ), and [Pd(dpp-bian)(Ph-mhan)](CF 3 SO 3 ) 2 ( 5 ). The resulting compounds were characterized by X-ray diffraction analysis, 1 H 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). A series of push-pull palladium(II) complexes containing redox-active bis(arylimino)acenaphthene (Ar-bian) and mono(arylhydrazino)acenaphthenone (Ar-mhan) have been synthesized and fully characterized.