The diphosphaazide complex (Mes*NPP)Nb(N[Np]Ar)(3) (Mes* = 2,4,6-tri-tert-butylphenyl, Np = neopentyl, Ar = 3,5-Me2C6H3), 1, has previously been reported to lose the P-2 unit upon gentle heating, to form (Mes*N)Nb(N[Np]Ar)(3), 2. The first-order activation parameters for this process have been estimated here using an Eyring analysis to have the values Delta H-double dagger = 19.6(2) kcal/mol and Delta S-double dagger = -14.2(5) eu. The eliminated P2 unit can be transferred to the terminal phosphide complexes P M(N[Pr-i]Ar)(3), 3-M (M = Mo, W), and [P Nb(N[Np]Ar)(3)](-), 3-Nb, to give the cyclo-P-3 complexes (P3)M(N[Pr-i]Ar)3 and [(P3)Nb(N[Np]Ar)(3)](-). These reactions represent the formal addition of a PP triple bond across a M P triple bond and are the first efficient transfers of the P2 unit to substrates present in stoichiometric quantities. The related complex (OC)(5)W(lMes*NPP)Nb(N[Np]Ar)(3), 1-W(CO)(5), was used to transfer the (P-2)W(CO)(5) unit in an analogous manner to the substrates 3-M (M = Mo, W, Nb) as well as to [(OC)(5)WP=-Nb(N[Np]Ar)(3)](-). The rate constants for the fragmentation of 1 and 1 -W(CO)5 were unchanged in the presence of the terminal phosphide 3-Mo, supporting the hypothesis that molecular P2 and (P2)W(CO)5, respectively, are reactive intermediates. In a reaction related to the combination of P P and M P triple bonds, the phosphaalkyne AdC P (Ad = 1-adamantyl) was observed to react with 3-Mo to generate the cyclo-CP2 complex (AdCP(2))Mo(N[Pr-i]Ar)(3). Reactions of the electrophiles Ph3SnCl, Mes*NPCI, and AdC(O)CI with the anionic, nucleophilic complexes [(OC)(5)W(P-3)Nb(N[Np]Ar)(3)](-) and [{(OC)(5)W}(2)(P-3)Nb(N[Np]Ar)(3)](-) yielded coordinated eta(2)-triphosphirene ligands. The Mes*NPW(CO)(5) group of one such product engages in a fluxional ring-migration process, according to NMR spectroscopic data. The structures of (OC)(5)W(P-3)W(N[Pr-i]Ar)(3), [(Et2O)Na][{(OC)(5)W}(2)-(P-3)Nb(N[Np]Ar)(3)], (AdCP(2))Mo(N[Pr-i]Ar)(3), (OC)(5)W(Ph3SnP3)Nb(N[Np]Ar)(3), Mes*NP(W(CO)(5))P3Nb(N[Np]Ar)(3), and {(OC)5W}(2)AdC(O)P3Nb(N[Np]Ar)(3), as determined by X-ray crystallography, are discussed in detail.