Linear Free Energy Relationships for Transition Metal Complex Chemistry: Opportunity or Pipe Dream?

We propose a computational framework for developing Taft-like linear free energy relationships to characterize steric effects on the catalytic activity of transition metal complexes. The framework uses the activation strain model and energy decomposition analysis to isolate electronic and geometric effects, and identifies structural descriptors to construct the linear relationship. We demonstrate proof-of-principle for CH activation with enzyme-inspired [Cu2O2]2+ complexes, each coordinated to two identical bidentate diamine N-donors. Electronic effects are largely similar across the chosen systems and geometric effects – quantified by strain energies – are accurately captured by a linear combination of two structural descriptors. A powerful linear free energy relationship emerges that is both transferable to asymmetrically substituted complexes and independent of choice of theory. We outline steps for expanding this approach to create a generalizable Taft framework for inorganic catalyst design.