Transition‐Metal‐Substituted Diphosphenes, XXVIII. – Synthesis and Structures of the First 1,2‐Diaza‐3,4‐diphosphetidines and (2E,8E)‐1,7‐Dioxa‐3,4,9,10‐tetraaza‐5,6,11,12‐tetraphospha‐2,8‐cyclododecadienes
(η5‐C5Me5)(CO)2FeP PMes*(Mes* 2,4,6‐tBu3C6H2) reacts with one equivalent of the Δ1‐1,2,4‐triazoline‐3,5‐diones (2a: R = Ph; 2b: R 4‐EtOC6H4) in benzene to give the first 1,2‐diaza‐3,4‐diphosphetidines 3a, b. When the same reaction is performed in diethylether the novel (2E,8E)‐1,7‐dioxa‐3,4,9,10‐tetraaza‐5,6,11,12‐tetraphospha‐2,8‐cyclododecadienes 4a, b are isolated as the sole products. The molecular structures of 3a and 4b are established by single‐crystal X‐ray analysis.