Synergistic Effects of Coordination Environments and Scaffold Rigidity on the Reactivity of Tripodal Bismuth(III) Complexes: A Computational Study

ABSTRACT

In this work, we have computationally investigated a series of tripodal Bi(III) complexes to understand how primary coordination site donor variation and secondary support from the ligand scaffold control Bi centered electrophilicity and metal ligand cooperativity. The results show that no single descriptor of electrophilicity is sufficient to explain reactivity toward H ₂ O, NH ₃ , and H ₂ . Instead, bond activation reflects a balance between Bi‐centered Lewis acidity, accessibility and directionality of the electrophilic site, covalency of Bi─X (X = donor atom coordination site), secondary scaffold support, and reorganizability. Geometrically defined, substrate‐accessible σ‐holes are identified for 3 and 3′ (X═O), while the remaining complexes are better described in terms of general Bi‐centered Lewis acidity. Energy decomposition analysis further reveals that strongly stabilizing substrate–complex interactions can be offset by substantial deformation penalties. A key finding is that replacing the lone pair donating N‐anchored scaffold ( 1 ‐ 3 ) with a π‐donating phenyl anchored scaffold ( 1' ‐ 3' ) lowers the barriers for the nitrogen and oxygen coordinating donor systems. In contrast, the nitroxide based phenyl anchored complex shows increased barriers because the Bi center becomes least accessible. Somewhat surprisingly, 1’ (X = N) exhibits a kinetically accessible H ₂ activation barrier. Our calculations also identify phenyl anchored tripodal ligands as promising secondary π‐donor scaffolds.