From Nitrogen (N) to Antimony (Sb): Comparing Bonding in Terminal Group 4 Pnictide Complexes

Isolating well-defined terminal pnictide complexes of Group 4 transition metals (Ti,Zr) remains a central challenge in fundamental organometallic chemistry, particularly for the heavier Group 15 congeners (As, Sb, Bi). This project defines a synthetic route to accessing a series of monoanionic, terminal Ti and Zr pnictide complexes using alkali metal pnictide precursors. Leveraging H2 extrusion as a congruent strategy, we reported unprecedented TiIV and ZrIV complexes with terminal stibido (Sb3-) ligands and investigated their bonding trends through crystallographic and computational analysis. Wiberg bond indices, bond metrics, and localized molecular orbitals (LMOs) reveal a progressive decrease in covalency as one moves As to Sb, offering deeper insight into how metal-pnictogen multiple bonding evolves down the periodic table. This work not only provides new synthetic routes for late pnictide complexes, but also advances our understanding of periodic trends in electronic structure and reactivity across transition metal-pnictogen frameworks.