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.