Computational study of the reactivity of palladacycles in catalytic applications

Boonseng, Sarote (2017) Computational study of the reactivity of palladacycles in catalytic applications. Doctoral thesis (PhD), University of Sussex.

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Abstract

This thesis presents a detailed theoretical/computational analysis using quantum chemistry to investigate the thermochemistry and reaction mechanisms of palladacycles that underpin experimental observations. The thesis begins by establishing a suitable computational methodology for the study of pincer palladacycles. It was found that Density Functional Theory (DFT) was suitable for the accurate reproduction of geometric structures and energetics by comparing a range of commonly used density functionals and basis sets with the X-ray crystal structures of symmetric pincer palladacycles. The detailed electronic structure of several pincer palladacycles was investigated using Complete Active Space Self-Consistent Field method (CASSCF) and it was shown that the dominant configuration was larger than 0.96, indicating that the ground state electronic structure has significant single-reference character. DFT was used to investigate the stability of symmetrical pincer palladacycles, and then by changing the donor ligand, unsymmetrical pincer palladacycles. The pincer palladacycle formation was investigated and it was found that the barrier to C-H activation was dependent on the ligand arm of the pincer that coordinates to PdCl2. Topological analysis was performed using Quantum Theory of Atoms In Molecules (QTAIM) for determining the strength and nature of the Pd and donor atom interactions, showing that the bond strength depends on the type of donor atom and trans influence in the pincer palladacycles. The mechanism for Pd(0) formation from both symmetrical and unsymmetrical pincer palladacycle pre-catalysts for catalysis in Suzuki-Miyaura carbon-carbon cross-coupling reactions was studied, and then with the introduction of base and the effect of solvent. It was shown that the key steps are transmetallation and reductive elimination processes, and differences in the overall Gibbs free energy and transmetallation barrier provide an explanation for observed catalytic activity. This has been in conjunction with experimental chemists.

Finally, the functionalisation of benzodiazepines was investigated in three conditions; with Pd(II)/Ru(II)-catalysts, with Pd(II)-catalysts and without catalyst. It was found that the Ru(II) photocatalyst with Pd(II)-catalyst is the best condition for functionalisation on benzodiazepines with the lowest energy barrier.

Item Type: Thesis (Doctoral)
Schools and Departments: School of Life Sciences > Chemistry
Subjects: Q Science > QD Chemistry > QD0146 Inorganic chemistry
Q Science > QD Chemistry > QD0241 Organic chemistry > QD0411 Organometallic chemistry and compounds
Depositing User: Library Cataloguing
Date Deposited: 09 Jun 2017 09:35
Last Modified: 09 Jun 2017 09:35
URI: http://sro.sussex.ac.uk/id/eprint/68416

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