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 (AqNH2 ), which is defined as a molecule of dual radical counter, are disclosed. 1-Amido-9,10-anthraquinone (AqNH- ) complexes of the types trans-[RuII (AqNH- )(PPh3 )2 (CO)Cl] (1), trans-[OsII (AqNH- )(PPh3 )2 (CO)Br] (2) and trans-[RuIII (AqNH- )(PPh3 )2 Cl2 ] (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 (AqNH SQ˙2- ). The reaction of 2 with I2 in CH2 Cl2 afforded a crystalline AqNH˙ complex of the type trans-[OsII (AqNH˙)(PPh3 )2 (CO)Br]+ I5 - ·½I2 (2+ I5 - ·½I2 ). AqNH˙ and AqNH SQ˙2- complexes of the types trans-[RuII (AqNH˙)(PPh3 )2 (CO)Cl]+ (1+ ), trans-[RuIII (AqNH˙)(PPh3 )2 Cl2 ]+ (3+ ), trans-[RuII (AqNH SQ˙2- )(PPh3 )2 (CO)Cl]- (1- ) and trans-[OsII (AqNH SQ˙2- )(PPh3 )2 (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 2+ I5 - ·½I2 , EPR spectroscopy and density functional theory (DFT) calculations. AqNH˙ instigates a 2c-3e pπ -dπ interaction and the length in 2+ I5 - ·½I2 , 1.978(5) Å, is relatively shorter than the OsII -NHAq - 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.