title: Structural Constraint and Flexibility in the Chemistry of Lewis-Acidic p-Block Atom-Based Molecules
creator: Sigmund, Lukas Maximilian
subject: ddc-540
subject: 540 Chemistry and allied sciences
description: Lewis acids are defined as electron pair acceptors, and the introduction of structural strain was shown a powerful lever to increase the Lewis acidity of p-block atom-based molecules. This dissertation presents experimental, quantum chemical, and data scientific contributions to the research area of p-block element-based Lewis acidity.   The reactivity of calix[4]pyrrolato aluminates (Cx[4]Al) was investigated experimentally. Cx[4]Al was found to heterolytically split the O-H bond of protic substrates (alcohols, carboxylic acids) in a reversible manner. With triplet dioxygen as substrate, Cx[4]Al forms an alkyl peroxido aluminate. A subsequent rearrangement reaction of the peroxido aluminates which yields α,β-unsaturated carboxylato aluminates was discovered and its reaction mechanism investigated. Furthermore, the reactivity of Cx[4]Al with nitrogen monoxide, nitrosobenzene, and phenyl isocyanate was studied. Characteristic for all reactions is an aluminum-ligand cooperative mechanism.   The  chemistry  of  the  calix[4]pyrrolato  ligands  was  expanded  to  gallium,  and  calix[4]pyrrolato gallates(III) (Cx[4]Ga) were synthesized and fully characterized. They are the first examples for ideally square planar-coordinated Ga(III) atoms. Cx[4]Ga’s reactivity with small molecules (e.g., CO2) as well as its redox chemistry were researched.   More than 250 small p-block atom-based molecules in square planar structural configuration  were  investigated  with  density  functional  theory  and  wavefunction-based quantum chemistry. Substituent effects on the planarization energies were discussed and related to the second-order Jahn-Teller theorem. Indeed, the square planar configurations can serve as transition states for the stereochemical inversion of the respective molecules. In addition to that, a new stepwise mechanism for stereoinversion was discovered.   Lastly, the FIA49k dataset, encompassing 48,986 fluoride ion affinities of molecules based on 13 different p-block elements, is presented herein. The data was generated with double-hybrid DFT calculations. It was used to train FIA-GNN, a graph neural network machine  learning  model  that  predicts  FIA  values.  FIA-GNN’s  usefulness  was  demonstrated in four different case studies.
date: 2024
type: Dissertation
type: info:eu-repo/semantics/doctoralThesis
type: NonPeerReviewed
format: application/pdf
identifier: https://archiv.ub.uni-heidelberg.de/volltextserverhttps://archiv.ub.uni-heidelberg.de/volltextserver/34642/1/Dissertation_Lukas_M_Sigmund.pdf
identifier: DOI:10.11588/heidok.00034642
identifier: urn:nbn:de:bsz:16-heidok-346426
identifier:   Sigmund, Lukas Maximilian  (2024) Structural Constraint and Flexibility in the Chemistry of Lewis-Acidic p-Block Atom-Based Molecules.  [Dissertation]     
relation: https://archiv.ub.uni-heidelberg.de/volltextserver/34642/
rights: info:eu-repo/semantics/openAccess
rights: http://archiv.ub.uni-heidelberg.de/volltextserver/help/license_urhg.html
language: eng