The reaction of 2-{2-(benzo[1,3]dioxol-5-yl)- diazo -4-methylphenol (HL) with [Ru(PPh3)(3)Cl-2] in ethanol resulted in the carbonylated ruthenium complex [RuL(PPh3)(2) (CO)] (1), wherein metal-assisted decarbonylation via in situ ethanol dehydrogenation is observed. When the reaction was performed in acetonitrile, however, the complex [RuL(PPh3)(2)(CH3CN)] (2) was obtained as the main product, probably by trapping of a common intermediate through coordination of CH3CN to the Ru(II) center. The analogous reaction of HL with [Ir(PPh3)(3)CI] in ethanol did not result in ethanol decarbonylation and instead gave the organoiridium hydride complex [IrL(PPh3)(2)(H)] (3). Unambiguous evidence for the generation of CO via rutheniumassisted ethanol oxidation is provided by the synthesis of the C-13-labeled complex, [Ru(PPh3)(2)]L((CO)-C-13)] (1A) using isotopically labeled ethanol, (CH3CH2)-C-13 OH. To summarize all the evidence, a ruthenium-assisted mechanistic pathway for the decarbonylation and generation of alkane via alcohol dehydrogenation is proposed. In addition, the in vitro antiproliferative activity of complexes 1-3 was tested against human cervical (HeLa) and human colorectal adenocarcinoma (HT-29) cell lines. Complexes 1-3 showed impressive cytotoxicity against both HeLa (half-maximal inhibitory concentration (IC50) value of 3.84-4.22 mu M) and HT-29 cancer cells (IC50 values between 3.3 and 4.5 mu M). Moreover, the complexes were comparatively less toxic to noncancerous NIH-3T3 cells.