Mo2o3 (Et2dtc) 2 (THF) 2I2, readily reduces various oxides. The Mo vio2+2 product of this reaction oxidizes TPP to triphenylphosphine oxide. The transient Mo(iv) species formed in the later reaction rapidly and irreversibly reacts with excess Mo vio2+2 to form the original Mo2 o3 4+ complex. These reactions can be also be coupled to provide catalytic oxygen transfer from PNO to TPP. This catalytic cycle can be monitored using a reverse phase high pressure liquid chromatography method that will also be discussed. The oxides chosen ranged from pyridine-N-oxide to the biological substrates: diphenylsufoxide, DMSO, nicotinamide-N-oxide, and biotin-S-oxide. Since Mo2o3 (Et2dtc) 2 (THF) 2I2 has the ability to abstract oxygen from these biologically significant substrates, it may result in the reconsideration of the role of Mo(V) complexes in catalytic cycles.