The synthesis of a series of (PPNRR)-P-Et (p(Et)p(NRR) = Et2P CH2 CH2P-CH2NRW) (CH2NRR)(2) R' = Ph or 2,4-difluorophenyl; R = R' = Ph or IPr) diphosphine ligands containing mono- and disubstituted pendant amine groups and the preparation of their corresponding molybdenum bis(dinitrogen) complexes trans-Mo(N-2)(2)(PMePh2)(2)(papNR)(9) is described. In situ IR and multinudear NMR spectroscopic studies monitoring the stepwise addition of triflic acid (HOT to trans-Mo(N-2)(2)(PMePh2)(2)(pEtpNR11) complexes in tetrahydrofuran at 40 degrees C show that the electronic and steric properties of the R and R' groups of the pendant amines influence whether the complexes are protonated at Mo, a pendant amine, a coordinated N, ligand, or a combination of these sites. For example, complexes containing monoaryl-substituted pendant amines are protonated at Mo and the pendant amine site to generate mono- and dicationic Mo H species. Protonation of the complex containing less basic diphenylsubstituted pendant amines exclusively generates a monocationic hydrazido (Mo(NNH2)) product, indicating preferential protonation of an N, ligand. Addition of HOTf to the complex featuring more basic diisopropyl amines primarily produces a monocationic product protonated at a pendant amine site, as well as a trace amount of dicationic Mo(NNH2) product that is additionally protonated at a pendant amine site. In addition, trans-Mo(N-2)(2)(PMePh2)(2)(depe) (depe = Et2PCH2CH2PEt2) was synthesized to serve as a counterpart lacking pendant amines. Treatment of this complex with HOTf generated a monocationic Mo(NNH2) product. Protonolysis experiments conducted on several complexes in this study afforded trace amounts of NH4RI Computational analysis of trans-Mo(N2)2(PMePh2)2(P EtpNV) complexes provides further insight into the proton affinity values of the metal center, N2 ligand, and pendant amine sites to rationalize differences in their reactivity profiles.