Pitfalls and Limitations in Group 6 Triamidophosphane Chemistry: Cage‐Closure Restrictions in Square‐Pyramidal Nitrido Complexes and Degradation via Spiro‐[4.4]‐λ 5 ‐Amidophosphorane Formation

The benzylene‐linked triaminophosphanes P(C 6 H 4 ‐ o ‐CH 2 NHXyl) 3 ([ A ]H 3 ) and P(CH 2 C 6 H 4 ‐ o ‐NHPh) 3 ([ B ]H 3 ) react with (Me 2 N) 3 Mo≡N to afford the square‐pyramidal nitrido complexes 1 and 2 , each comprising one residual dimethylamido moiety and one uncoordinated ligand sidearm. Only the [ A ]‐coordinated complex 1 was found to eliminate the remaining dimethylamido ligand on heating. Instead of the closed‐cage molybdenum(VI) nitrido complex [ A ]Mo≡N, cyclometalated molybdaziridine 3 was isolated, as the syn alignment of the uncoordinated sidearm and nitrido ligand in 1 inhibits a productive cage‐closure reaction. By using [NPN]‐coordinated model complexes, analogous syn arrangements were found not only for molybdenum, but also for the related tungsten nitrido complexes and the group 5 imides. Attempts to access the closed‐cage Mo VI nitrido comlex [ A ]Mo≡N by transmetalation between [ A ]Sn( n Bu) ( 9 ) and ( t BuO) 3 Mo≡N led to the formation of spiro‐[4.4]‐λ 5 ‐amidophosphorane 10 . These results contrast with the findings made for azatranes and methylene‐linked exo ‐ P ‐configured triamidophosphane complexes.