Arylamino radical complexes of ruthenium and osmium: dual radical counter in a molecule.

Radical and non-radical ruthenium and osmium complexes of 1-amino-9,10-anthraquinone (AqNH), which is defined as a molecule of dual radical counter, are disclosed. 1-Amido-9,10-anthraquinone (AqNH) complexes of the types trans-[Ru(AqNH)(PPh)(CO)Cl] (1), trans-[Os(AqNH)(PPh)(CO)Br] (2) and trans-[Ru(AqNH)(PPh)Cl] (3) were isolated. AqNH of 1-3 is redox active and undergoes oxidation reversibly at +(0.05-0.35) V to the 1-amino-9,10-anthraquinone radical (AqNH˙) and reduction at -(0.86-1.60) V to the 1-amido-9,10-anthrasemiquinonate anion radical (AqSQ˙). The reaction of 2 with I in CHCl afforded a crystalline AqNH˙ complex of the type trans-[Os(AqNH˙)(PPh)(CO)Br]I·½I (2I·½I). AqNH˙ and AqSQ˙ complexes of the types trans-[Ru(AqNH˙)(PPh)(CO)Cl] (1), trans-[Ru(AqNH˙)(PPh)Cl] (3), trans-[Ru(AqSQ˙)(PPh)(CO)Cl] (1) and trans-[Os(AqSQ˙)(PPh)(CO)Br] (2) were generated chemically/electrochemically in solution. The electronic states of the complexes were authenticated by single crystal X-ray structure determinations of 1, 2·5/4 toluene, 3 and 2I·½I, EPR spectroscopy and density functional theory (DFT) calculations. AqNH˙ instigates a 2c-3e p-d interaction and the length in 2I·½I, 1.978(5) Å, is relatively shorter than the Os-NH length, 2.037(2) Å, while the Aq-NH˙ bond, 1.365(8) Å, is longer than the Aq-NH bond, 1.328(3) Å. DFT calculations predicted that the atomic spin is delocalized over the ligand backbone (1, 56%) particularly in one of the p-orbitals of the nitrogen and the metal atoms of the 1 and 2 ions, while the spin is dominantly localized on the anthraquinone fragment of the 1 and 2 ions. TD DFT calculations were employed to elucidate the origins of the lower energy absorption bands of the neutral complexes. Hypsochromic shifts of the UV-vis-NIR absorption maximum during 1→1, 2→2 and 3→3 conversions were recorded by spectroelectrochemical measurements.