Predictive Models for Ligand Effects on a Reactive Al-Containing Radical Intermediate from Multivariate Linear Regression Analysis

Our lab has studied a complex with an Al–Fe bond capable of cooperative substrate activation processes. This reactivity was previously found to depend on Al–Fe homolytic bond dissociation followed by substrate coordination to the AlIII center of the resulting redox noninnocent radical intermediate. The current study investigates ligand influences on the Al–Fe bond dissociation free energy (BDFEAl–Fe) and the Gibbs free energy of H2O coordination at aluminum (ΔGOH2) for a series of variants with systematic changes in their ligand substitution patterns. DFT calculations combined with multivariate linear regression analysis provided predictive models for ligand effects on both BDFEAl–Fe and ΔGAl–OH2 for three synthetically tunable positions in the molecular architecture when using appropriate electronic (σpara, σmeta) and steric (wSterimol, %Vbur) descriptors. Chemical interpretations of the predictive models were facilitated by the use of these intuitive descriptors. Linear scaling relationships relating BDFEAl–Fe and ΔGOH2 provided further insight. We expect our findings to inform designs of future Al-containing heterobinuclear complexes for small molecule activation processes and cleavage reactions of strong or inert bonds.