The dichlorophosphido complexes ([eta]5-C5Me5)(CO)2M-PCl2 (2a: M = Fe; 2c: M = Ru) react with two equivalents of Ph2C = NSiMe, to yield the first [eta]1-2,4-diaza-3-phosphapenta-1,4-dien-3-yl complexes (4a,c). Intermediates ([eta]5-C5Me5)(CO)2M-P(Cl)(N = CPh2) (3a,c) are detected by 31P{1H} NMR spectroscopy, the preparation of pure 3a, however, failed. The products 4a,c have been characterized by elemental analysis as well as spectroscopic data (IR, 1H, 13C, 31P NMR, MS). The molecular structure of 4a has been elucidated by single X-ray analysis.