The influence of ligand substitution on the reactivity of iron-β-diketiminate complexes

• Main Author: Linford-Wood, Thomas George
• Format: Dissertation
• Language: English
• Published: University of Bath 2023

The ß-diketiminate (BDK) ligand has become one of the most ubiquitous scaffolds in organometallic chemistry. This is a function of it being tunable and proficient at stabilising reactive, low-coordinate complexes. With the emerging challenges associated with diminishing precious metal resources, discovering analogous reactivity utilising abundant elements is a desirous objective of chemical research. Hence, many iron-BDK complexes have been developed and ground-breaking examples are highlighted in chapter 1. Ligand modulation leads to altered spatial confinement. In some cases, this facilitates orthogonal reactivity- a recurrent theme throughout the thesis. Chapter 2 details the first example of iron-catalysed hydrogen/deuterium exchange of silanes with deuterium gas. By variation of ligand environment, near complete deuterium incorporation is observed for primary, secondary, and tertiary silanes, tertiary siloxanes and pinacolborane. An accompanying mechanistic study reveals an iron-deuteride is responsible for isotope exchange. Stoichiometric reactions facilitate isolation of a new class of iron-hydride complexes, with record-breaking downfield 1H NMR resonances. Studies into the iron-catalysed transfer hydrogenation (TH) of carbon-carbon double bonds are reported in chapter 3. Using benign TH reagents (nbutanol and poly(methylhydrosiloxane) (PMHS)), a range of allyl arenes, styrenes and aliphatic olefins undergo reduction. By careful selection of deuteron and hydride sources, regioselective transfer hydrodeuteration can be achieved. In the absence of alkene substrate, dehydrocoupling of various alcohols with PMHS is observed, generating high yields of hydrogen gas within 30 minutes. Chapter 4 describes the optimisation of a 2nd generation chiral BDK, derived from N -aryl-containing flanking groups. Density functional theory is deployed as a predictive tool, suggesting the corresponding iron(II)-hydride, bearing this ligand, will undergo enantioselective insertion of carbon-carbon double bonds. Pro-ligand optimisation, along with its associated iron complexes, is described, culminating in the first iron-BDK-catalysed asymmetric hydrofunctionalisation. Polymeric materials featuring cage-dense moieties are rarely reported. This is surprising given they demonstrate excellent thermal properties. The major challenge is finding stable and accessible cagederived monomers. Chapter 5 details the synthesis and characterisation of an array of phosphazabicyclo[2.2.2]octane polymers, containing (aryl)dichlorophosphine co-monomers. In situ reaction monitoring experiments provide insight into the polymerisation mechanism, along with the impact of electrondensity on reaction rate.