Ruthenium Complexes of Analogues of the Antitumor Antibiotic Streptonigrin

The complexes Ru(L1−CH3)(CO)3Cl, RuL2(CO)2Cl2, and RuL3(CO)2Cl2 (L1= 6-methoxy-5,8-quinolinedione, L2 =
7-amino-6-methoxy-5,8-quinolinedione, L3 = 6,6‘-dimethoxycarbonyl-2,2‘-bipyridine) were prepared by reaction of
L1−L3 with the tricarbonyldichlororuthenium(II) dimer. L1−L3 act as bidentates through the ortho oxygen atoms,
the pyridyl nitrogen and the adjacent quinone oxygen, and the bipyridyl nitrogens, respectively. RuL3(CO)2Cl2 is
characterized by X-ray crystallography. 15N NMR correlation spectra give upfield shifts of around 60 ppm for the
pyridyl nitrogens that are coordinated to the metal, while 13C NMR correlation spectra give a downfield shift of 10
ppm for the quinone carbonyl group that is coordinated to the metal. The electrochemistry of RuL2(CO)2Cl2 is
examined, and the implications for the formation of metal complexes of the antitumor antibiotic streptonigrin, which
cleaves DNA in the presence of metal ions, are discussed.