(eta-5-C5Me5)(CO)2FePH2 (5), prepared from (eta-5-C5Me5)(CO)2Fe-P(SiMe3)2 and ethanol, reacts with one equivalent of ClP = C(SiMe3)2 to give the diphosphirane (eta-5-C5Me5)(CO)2Fe-P-C(SiMe3)2-PH (8). Compound 8 is converted into the iron chromium complex [(eta-5-C5Me5)(CO)2Fe-P-C(SiMe3)2-PH]-Cr(CO)5 (9). In contrast, the reaction of 5 with two equivalents of ClP=C(SiMe3)2 results in the formation of the cyclotriphosphane [(eta-5-C5Me5)(CO)2Fe-P]2P[CH(SiMe3)2] (12). The molecular structure of 9 is elucidated by single-crystal X-ray analysis.