The diphosphenyl complex [Fe]P:PR [R = 2,4,6-(Me3C)3C6H2, [Fe] = (h5-C5Me5)Fe(CO)2] reacts with an equimolar amt. of sulfur to yield the first thioxo-l5-diphosphenyl complex [Fe]P(S):PR (I). Heating of I in boiling benzene affords the metal functionalized thiadiphosphirane II (Q = S). Similarly the selenoxo-l5-diphosphenyl complex [Fe]P(Se):PR and selenadiphosphirane II (Q = Se) are synthesized. The mol. structure of I has been elucidated by single crystal x-ray anal.