Pyrolysis and oxidation reactions of the iridium precursor, (methylcyclopentadienyl)(1,5 -cyclooctadiene)iridium (I), were studied to identify the role of O-2 in chemical vapor deposition film growth. A toluene solution of (methylcyclopentadienyl)(1,5-cyclooctadiene)iridium (1) was used in a direct liquid injection chemical vapor deposition process with O-2 to deposit iridium films on SiO2 and TiN(111) substrates. The precursor decomposition studies revealed O-2 decreases the reaction temperature of (methylcyclopentadienyl)(l,5 -cyclooctadiene)iridium (1) from near 760 K to temperatures below 465 K. Oxidation of the precursor ligands acts to prevent greater than 99% of the carbon from incorporating into the deposited him, making the growth surface more reactive. The precursor and oxygen react to form CO, CO2 and H2O. Pure iridium films were deposited on SiO2 and TiN(III) substrates at temperatures between 550 and 625 K. Under identical conditions, the film nucleation and coalescence rates are nearly 2 times higher on the TiN(111) substrate with 0.22 torr O-2. The ratio of (111) to (200) X-ray diffraction intensities resembled Ir powder for films deposited on SiO2, the same ratio was more than 9 times larger than that of Ir powder for Ir films produced on TiN(111). Decreasing the oxygen partial pressure from 0.66 to 0.22 torr resulted in a 75% reduction in the film growth rate and a 40% reduction in film roughness. Conformal (step coverage approaching unity) iridium films were produced at 550 K in aspect ratio 1-0.25 mum vias in SiO2 and in aspect ratio 2.5-0.35 mum vias in TIN(111).