Computational analysis of bonding and reactivity of sterically demanding magnesium complexes

Low coordinate, low oxidation state magnesium complexes have emerged as attractive alternatives to traditional transition-metal reagents, exhibiting remarkable proficiency in bond activation and a wide range of catalytic transformations. Their high natural abundance, low toxicity, and distinct electronic structures make magnesium-based reagents particularly attractive for the development of sustainable chemistry. This thesis presents a comprehensive computational investigation into the bonding, structure, and reactivity of sterically demanding magnesium complexes in low coordination numbers and oxidation states. Using a combination of density functional theory (DFT), extended tight-binding methods (xTB), and advanced bonding analyses including natural bond orbital (NBO), Quantum theory of atoms in molecules (QTAIM), and dispersion-corrected approaches, this work elucidates the electronic origins of reactivity and the subtle interplay between ligand sterics, dispersion forces, and thermodynamic stability. Chapter 1 provides an overview of main group chemistry, providing insights into their synthesis, bonding and reactivity with particular emphasis on low coordinate and low oxidation state magnesium complexes. Chapter 2 focuses on the structure and bonding of isomeric β-diketiminate magnesium(II) carbene complexes, offering insight into electronic structure variations arising from ligand isomerism. Chapter 3 examines low-coordinate β-diketiminate magnesium(II) chalcogenide complexes, highlighting the critical roles of ligand bulk and dispersion interactions in stabilising these species and modulating their bonding characteristics. Chapter 4 will delve into the mechanism of dihydrogen activation by a magnesium(I) oxide while simultaneously exploring the role of bulk on the reaction thermodynamics, while in Chapter 5, the mechanistic pathway for the reduction of diphenylacetylene by a magnesium(I) dimer has been discussed providing insight into the thermochemistry of the reaction, the effect of dispersion and effect of bulk on the ligand backbone.