Synthesis and Thermolysis of a Phosphorus(III) Oxalate. Evidence for the Generation of an Arylphosphimidene Oxide The phosphorus(III) oxalate pictured (1) was prepared via the reaction of Ar’PGl(2) (Ar’ = 2,4,6-t-Bu(3)C(6)H(2)) with Ag2C2O4. The existence of a planar five-membered PO2C2 ring was demonstrated by X-ray crystallography. The intermediacy of the phosphinidene oxide Ar’PO in the thermolysis of 1 is discussed.