Computational investigations of homogeneous catalysis and spin-state energetics in Fe(II) and Co(III) complexes

Abstract

This thesis focuses on the testing and use of quantum-chemical modelling to describe and study Fe(II) and Co(III) complexes, and in particular their spin-state behaviour and efficacy in homogeneous catalysis.

An Fe(II)-catalysed transfer-hydrogenation reaction was investigated with density functional theory (DFT). This project was in close collaboration with experimentalists in the Webster group at the University of Bath. To ensure an accurate approach was employed, a rigorous benchmarking evaluation was carried out against available and closely related experimental data (Chapter 2). This identified a reliable DFT approach to study the catalytic transfer-hydrogenation reaction with (Chapter 3). Modelling of this reaction revealed that careful assessment of the chemical model was required to account fully for the experimental observations, namely in accounting for a selectivity towards transfer-hydrogenation over hydroboration and dehydrocoupling. The identification of supramolecular oligomerization of reagents was an important component of the final chemical model.

The other reaction of interest in this work is Co(III) carboxylate-assisted C–H functionalization. In this case, a benchmarking study against experimentally-derived spin-state energetics of Co(III) complexes was carried out to evaluate quantum-chemical approaches in the context of Co(III) catalysis (Chapter 4). DFT, NEVPT2 and DLPNO-CCSD(T) were assessed in this regard, and DLPNO-CCSD(T) was found to be the most accurate performer of the three types of methods. This level of theory was then used to yield reference energetics when looking at an archetypal Co(III) carboxylate-assisted C–H functionalization reaction, and against this reference profile, the performance of DFT was assessed (Chapter 5). This identified a computational protocol which allowed for the modelling and assessment of the full catalytic C–H functionalization reaction.