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

Abstract

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)2Cl2] (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 (AqNHSQ˙2-). The reaction of 2 with I2 in CH2Cl2 afforded a crystalline AqNH˙ complex of the type trans-[OsII(AqNH˙)(PPh3)2(CO)Br]+I5-·½I2 (2+I5-·½I2). AqNH˙ and AqNHSQ˙2- complexes of the types trans-[RuII(AqNH˙)(PPh3)2(CO)Cl]+ (1+), trans-[RuIII(AqNH˙)(PPh3)2Cl2]+ (3+), trans-[RuII(AqNHSQ˙2-)(PPh3)2(CO)Cl]- (1-) and trans-[OsII(AqNHSQ˙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.