Small Molecule Activation and Functionalisation Methodologies at Heptapnictogen Zintl Clusters

Abstract

Zintl Clusters are polyatomic anionic clusters that comprise of elements from the p-block. The heptapnictogen trianionic Zintl clusters [Pn7]3– (Pn = P, As) bear structural similarities to elemental phosphorus or arsenic respectively, which tend to be insoluble in common laboratory solvents. Zintl clusters, functionalised with main group moieties are more soluble in such solvents and can provide an insight into the solution state reactivity of functionalised bulk materials. In Chapter 2 we outline the synthesis of tetrel-functionalised Zintl clusters (R3Te)3Pn7 (Pn = P, Te = Ge, Sn; Pn = As, Te = Si) and investigations into their reactivity towards isocyanates and carbon dioxide. It was found that isocyanates could be captured between all three Pn–Te bonds through either C=N or C=O bond activation, depending on the electronic properties of the isocyanate. The synthesis of a new [As11]5– core is detailed which shows a significant difference in both shape and charge when comparing to previously reported [Pn11] cluster cores. Further, the reactivity of (Me3Ge)3P7 and (Me3Si)3P7 towards azides revealed a novel methodology for installing nitrogen functionality exo- to the cluster core through the insertion of [RN] units between one or more P–Te bonds. Although, (Me3Si)3P7 preferentially formed the tris-inserted product and (Me3Ge)3P7 formed the mono-inserted product, controlling the reaction stoichiometry afforded first example of the selective synthesis of a mono-, bis- and tris-inserted product using a tris-functionalised [P7] cluster. NBO (natural bonding orbital) and AIMS (atoms in molecules) analysis revealed charge reversal at the bridging phosphorus atoms from negative to positive, consistent with a net oxidation at the cluster. Finally, K3As7 was found to fragment when treated with benzyl azide, affording the novel arsolide [AsN(CPh)N(CPh)]– ring. The electronic transitions within the ring were studied by TD-DFT (time dependant density functional theory) studies and the aromaticity was indexed against [C5H5]– and other similar heterocycles using NICS (nuclear independent chemical shift) studies. Preliminary investigations into the coordination of [AsN(CPh)N(CPh)]– with Co(II) are also detailed.

Date of Award	19 Nov 2024
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Imogen Riddell (Main Supervisor) & Robert Dryfe (Co Supervisor)