Three new diruthenium oxyanion complexes have been prepared, crystallogiaphically characterized, and screened for their potential to photochemically unmask a reactive Ru-Ru-=O intermediate. The most promising candidate, Ru-2(chp)(4)ONO2 (4, clip = 6-chloro-2-hydroxypyridinate), displays a set of signals centered around m/z = 733 amu in its MALDI-TOF mass spectrum, consistent with the formation of the [Ru-2(chp)(4)O](+) ([6](+)) ion. These signals shift to 735 amu in 4*, which contains an O-18-labeled nitrate. EPR spectroscopy and headspace GC-MS analysis indicate that NO2 center dot is released upon photolysis of 4, also consistent with the formation of 6. Photolysis of 4 in CH2Cl2 at room temperature in the presence of excess PPh3 yields OPPh3 in 173% yield; control experiments implicate 6, NO2 center dot, and free NO3- as the active oxidants. Notably, Ru-2(chp)(4)Cl (3) is recovered after photolysis. Since 3 is the direct precursor to 4, the results described herein constitute the first example of a synthetic cycle for oxygen atom transfer that makes use of light to generate a putative metal oxo intermediate.