Diagnosing the Redox Character of Bond Activation by Main Group Centers: Reductive Addition vs Redox-Neutral Insertion as a Case Study

The reductive addition of small molecules to low-valent main-group centers has recently started to emerge, yet their redox labeling is often inferred from qualitative electronegativity arguments and partial-charge trends. Here, we use a recent representative example, i.e., Zn–Zn bond cleavage by Si^II and Al^I main-group carbene analogues as a motivating case study and place it in a broader comparative computational analysis alongside conventionally oxidative H_{2 addition. We show that electronegativity- and partial-charge-based descriptors are strongly scheme- and scale-dependent and therefore insufficiently robust to diagnose redox character. In contrast, electron density- and wave-function-based metrics provide a consistent assignment across systems and reveal a central role of ligand electronics. Particularly, extensive ligand-assisted delocalization of the lone pair at Si leads to retention of a formal +2 oxidation state upon addition of Cp*ZnZnCp*, establishing the process as redox-neutral. More generally, our results identify ligand design as a practical handle to tune the reductive character of addition processes and provide a transferable, computation-led framework for assigning redox character in emerging main-group reactivity.}