title: Synthesis and Characterization of Silicon Polyoxolenes
creator: Maskey, Rezisha
subject: ddc-540
subject: 540 Chemistry and allied sciences
description: Tris(catecholato)silicate dianions, a compound class that is already known for over a century, can be readily prepared by reacting sand with catechol under basic conditions. Strikingly, the two-electron-oxidized derivative – silicon tris(perchloro)dioxolene 1Cl – has been recently accessed, representing a thermally stable, neutral triplet diradical and the first non-metal complex with redox-active and mixed-valence substituents. In the present work, the redox properties of 1Cl are investigated and by the synthesis of the corresponding monoradical anion [1Cl]•−, the redox series of tris(catecholato)silicates in general is completed. With cyclic voltammetry the redox potentials E1/2 = 0.43 V and 0.88 V (vs. Fc/Fc+) were finally determined. Comparing the redox potentials of 1Cl with free tetrachloro-o-benzoquinone, a tremendous shift of about 1.2 V becomes apparent. Moreover, 1Cl is applicable as efficient redox catalyst.   By varying the quinone ligands and the silicon source, further homo- and heteroleptic derivatives are prepared. Variable temperature EPR measurements disclose the existence of diradicals with a triplet ground state.   With a more profound understanding of the monomeric species, the synthesis is extended to higher nuclearity. A straightforward approach is established by introducing substituted 2,5-dihydroxy-p-benzoquinone (H2dhbqY) as [dhbqY][Na@15c5]2 (Y = Cl, Br, Ph, NO2) salts and mixing with bis(catecholato)silanes 2X (X = Cl, Br, CF3, iPr) to obtain the dinuclear species [4X,Y][Na@15c5]2, which are robust to coordinating environments. By selective combination of more electron-rich 2X and electron-poor dhbq linkers diradicaloid complexes [4X,Y]2− (X = Cl, iPr and Y = Cl, Br, NO2) were obtained and characterized. The opposite extreme with the smallest diradical character was accomplished by combining electron-poor 2CF3 and electronrich dhbqPh. The underlying design principle is further disclosed by computational analyses. Conclusively, this one-step protocol grants access to dimeric silicon polyoxolenes with control over and fine-tuning of the spin ground state. Lastly, preliminary results are obtained for the trimeric structures by implementing the six-fold deprotonated tritopic linker 2,3,6,7,10,11-hexahydroxytriphenylene (H6hhtp) with 2Cl. The results gathered in this work present a fundamental understanding of silicon-bridged polyoxolenes and thus are valuable extensions based on a non-metal main group element to known works based on transition metals.
date: 2023
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/33092/1/Dissertation_Rezisha_Maskey_2023.pdf
identifier: DOI:10.11588/heidok.00033092
identifier: urn:nbn:de:bsz:16-heidok-330929
identifier:   Maskey, Rezisha  (2023) Synthesis and Characterization of Silicon Polyoxolenes.  [Dissertation]     
relation: https://archiv.ub.uni-heidelberg.de/volltextserver/33092/
rights: info:eu-repo/semantics/openAccess
rights: http://archiv.ub.uni-heidelberg.de/volltextserver/help/license_urhg.html
language: eng