The “constrained geometry” zirconaaziridines Me₄C₅SiMe₂N(tBu)Zr-(eta-2)-[N(Ph)CH(Ph)](PMe₂R) have been synthesized and the R = Ph derivative has been structurally characterized by X-ray crystallography. Treatment of these compounds with carbodiimides results in insertion into the Zr-C and Zr-N bonds, while treatment with diphenylacetylene results in insertion into the Zr-C bond only. Kinetic data for these irreversible reactions indicate that phosphine dissociation must occur prior to carbodiimide or alkyne insertion. Insertion of these electrophiles into the analogous bis(cyclopentadienyl)zirconaaziridine proceeds several orders of magnitude more slowly than insertion into the “constrained geometry” complex. Comparison of kinetic data for the bis(cyclopentadienyl) vs. “constrained geometry” complexes allows quantitative descriptions of ligand binding in these systems.