Tris(pyronato)- and Tris(pyridonato)-ruthenium(III) Complexes and Solution NMR Studies

The water-soluble RuIII maltolato, ethylmaltolato, and pyridonato complexes, Ru(O−O‘)3 (O−O‘ = ma (1a), etma
(1b), pyd (2a)), were synthesized (Hma = 3-hydroxy-2-methyl-4-pyrone, Hetma = 2-ethyl-3-hydroxy-4-pyrone,
Hpyd = 3-hydroxy-1,2-dimethyl-4-pyridone). The complexes were characterized by elemental analysis, NMR and
IR spectroscopies, MS, solution conductivity, and cyclic voltammetry, and in the case of Ru(ma)3, by X-ray
crystallography, which revealed a mer configuration. The paramagnetic 1H NMR resonances of 1a, 1b, and 2a
were assigned using 2D methods (1H COSY and 1H-13C HMQC) and variable-temperature 1H NMR data and
showed that 1a and 1b exist in aqueous solution predominantly as a mer isomer, while 2a is a mixture of mer and
fac isomers. Although a 13C NMR spectrum could not be measured directly for 1a, a partial 13C spectrum was
generated from the 1H-13C HMQC spectrum. Complexes 1a and 1b were tested for anti-proliferatory activity against
the human breast cancer cell line MDA-MB-435S and gave IC50 values of 140 and 90 μM, respectively.