Rhenium carbonyl complexes of 2,6-diazaanthracene-9,10-dione(daad): spectroelectrochemistry of BrRe(CO)4daad

An analysis of the X-ray structure, vibrational and electronic spectra of BrRe(CO)4daad, 2, and a spectroscopic study of the radical anion 2radical dot− are presented (daad=2,6-diazaanthracene-9,10-dione). Strong π-stacking is seen in the crystal structure of 2. Electronic absorption, resonance Raman vibrational analysis and electrochemistry of 2 support an assignment of the HOMO and LUMO to a predominately metal dπ and ligand π* orbital (localised on the quinoidal ring), respectively. There is poor orbital overlap between donor Re (dπ) and acceptor ligand π* MOs. 2 undergoes a ligand-based reduction process at −0.24 V vs. decamethylferrocene to give 2radical dot− which was investigated by spectroelectrochemistry and isolated as the [Cp2Co]+ salt. Insoluble [XRe(CO)3daad]n and unstable XRe(CO)3(daad)2 complexes, where X=Br or Cl, were also identified.