The reaction of m-chloroperbenzoic acid with some pentacarbonyltungsten complexes of (E)-diphosphene having the O-P=P skeleton afforded a new type of complexes of phosphorus esters. The structures of these compounds were identified by MS, NMR, IR and elemental analysis. Irradiation of a carbonyltungsten complex of (E)- diphosphene led to photoisomerization. The resultant complex of (Z)- diphosphene was characterized by ^3^1P and ^1HNMR.

Key words: CARBONYL GROUP, TUNGSTEN COMPLEX, ORGANO PHOSPHORUS COMPOUNDS, OXIDATION, PHOTO-ISOMERIZATION