The reaction of N-(trimethylsilyl) phosphoranimine Cl3PdNSiMe3 (1) with (Bu3P)-Bu-n or Ph3P yields the N-(dichlorophosphino) phosphoranimines (Bu3PdNPCl2)-Bu-n (4a) or Ph3PdNPCl2 (4b), respectively. Detailed studies of this reaction indicate a mechanism that involves the reductive dechlorination of 1 by the tertiary phosphine to yield nBu(3)PCl(2) (5a) or Ph3PCl2 (5b) with the apparent formation of the transient chlorophosphinimine ClPdNSiMe3 ( 6), followed by condensation of 5a or 5b with 1 to form 4a or 4b and Me3SiCl. Convincing evidence for the proposed mechanism was revealed by studies of the analogous reaction between the N-(triphenylsilyl) phosphoranimine Cl3PdNSiPh3 (8) with nBu(3)P and Ph3P. These reactions quantitatively generated 5a and 5b and also allowed the correspondingly more stable chlorophosphinimine ClPdNSiPh3 (10) to be identified.