[Ar2N3]Mo(N)(O-t-Bu), which contains the conformationally rigid pyridine-based diamido ligand, [2,6-(ArNCH2)(2)NC5H3](2-) (Ar = 2,6-diisopropylphenyl), can be prepared from H-2[Ar2N3], butyllithium, and (t-BuO)(3)Mo(N). [Ar2N3]Mo(N)(O-t-Bu) serves as a catalyst or precursor for the catalytic reduction of molecular nitrogen to ammonia in diethyl ether between 78 and 22 degrees C in a batchwise manner with CoCp2* as the electron source and Ph2NH2OTf as the proton source. Up to similar to 10 equiv of ammonia can be formed per Mo with a maximum efficiency in electrons of similar to 43%.