Molybdenum dinitrogen complexes are presented which are supported by novel hybrid tripod ligands of the type Me-C(CH2PPh2)(2)((CH2PPr2)-Pr-i) (trpd-1) and H-C(CH2PPh2)((CH2PPr2)-Pr-i)(2) (trpd-2) having mixed clialkylphosphine/diarylphosphine donor groups. Reaction of the ligand trpd-1 with [MoI3(thf)(3)] followed by sodium amalgam reduction in the presence of the dppm gives the dinitrogen complex [Mo(N-2)(trpd-1)(dmpm)] where trpd-1 is coordinated in a kappa(3) fashion. The complex exhibits a moderate activation of N-2 which enables its protonation under retention of the pentaphosphine ligation. Replacement of dmpm by the sterically more demanding coligand dppm is found to hamper coordination of N-2 and leads to [Mo(trpd-1)(dppm)], the first structurally characterized five-coordinate Mo(0) complex with a phosphine-only ligand sphere. Employing the ligand trpd-2 along with the diphosphines dmpm and dppm in an analogous synthetic route results in a mixture of the bis(dinitrogen) complexes trans-[Mo(N-2)(2)(kappa(2)-trpd-2)(diphosphine)] and trans-[Mo(N-2)(2)(iso-kappa(2)-trpd-2)(diphosphine)] where the tripod ligand trpd-2 coordinates with two phosphine arms and one phosphine group (PPh2 or (PPr2)-Pr-i, respectively) is free. Similar results are obtained with the pure alkyl- and arylphosphine tripod ligands H-C((CH2PPr2)-Pr-i)(3) (trpd-3) and H-C(CH2PPh2)(3) (tdppmm), leading to trans-[Mo(N-2)(2)(kappa(2)-trpd-3)(diphos)] and trans-[Mo(N-2)(2)(kappa(2)-tdppmm)(dmpm)], respectively. The electronic and steric reasons for the experimental findings are considered, and the implications of the results for the area of synthetic nitrogen fixation with molybdenum phosphine systems are discussed.