Authors:	Moritz, Ralf
Title:	Synthesis, properties and application of polyphenylene phosphonium salts
Online publication date:	20-Apr-2015
Year of first publication:	2015
Language:	english
Abstract:	The central objective of this work was to generate weakly coordinating cations of unprecedented molecular size providing an inherently stable hydrophobic shell around a central charge. It was hypothesized that divergent dendritic growth by means of thermal [4+2] Diels-Alder cycloaddition might represent a feasible synthetic method to circumvent steric constraints and enable a drastic increase in cation size.rnThis initial proposition could be verified: applying the divergent dendrimer synthesis to an ethynyl-functionalized tetraphenylphosphonium derivative afforded monodisperse cations with precisely nanoscopic dimensions for the first time. Furthermore, the versatile nature of the applied cascade reactions enabled a throughout flexible design and structural tuning of the desired target cations. The specific surface functionalization as well as the implementation of triazolyl-moieties within the dendrimer scaffold could be addressed by sophisticated variation of the employed building block units (see chapter 3). rnDue to the steric screening provided by their large, hydrophobic and shape-persistent polyphenylene shells, rigidly dendronized cations proved more weakly coordinating compared to their non-dendronized analogues. This hypothesis has been experimentally confirmed by means of dielectric spectroscopy (see chapter 4). It was demonstrated for a series of dendronized borate salts that the degree of ion dissociation increased with the size of the cations. The utilization of the very large phosphonium cations developed within this work almost achieved to separate the charge carriers about the Bjerrum length in solvents of low polarity, which was reflected by approaching near quantitative ion dissociation even at room temperature. In addition to effect the electrolyte behavior in solution, the steric enlargement of ions could be visualized by means of several crystal structure analyses. Thus an insight into lattice packing under the effect of extraordinary large cations could be gathered. rnAn essential theme of this work focused on the application of benzylphosphonium salts in the classical Wittig reaction, where the concept of dendronization served as synthetic means to introduce an exceptionally large polyphenylene substituent at the -position. The straightforward influence of this unprecedented bulky group on the Wittig stereochemistry was investigated by NMR-analysis of the resulting alkenes. Based on the obtained data a valuable explanation for the origin of the observed selectivity was brought in line with the up-to-date operating [2+2] cycloaddition mechanism. Furthermore, a reliable synthesis protocol for unsymmetrically substituted polyphenylene alkenes and stilbenes was established by the design of custom-built polyphenylene precursors (see chapter 5).rnFinally, fundamental experiments to functionalize a polymer chain with sterically shielded ionic groups either in the pending or internal position were outlined within this work. Thus, inherently hydrophobic polysalts shall be formed so that future research can invesigate their physical properties with regard to counter ion condensation and charge carrier mobility.rnIn summary, this work demonstrates how the principles of dendrimer chemistry can be applied to modify and specifically tailor the properties of salts. The numerously synthesized dendrimer-ions shown herein represent a versatile interface between classic organic and inorganic electrolytes, and defined macromolecular structures in the nanometer-scale. Furthermore the particular value of polyphenylene dendrimers in terms of a broad applicability was illustrated. This work accomplished in an interdisciplinary manner to give answer to various questions such as structural modification of ions, the resulting influence on the electrolyte behavior, as well as the stereochemical control of organic syntheses via polyphenylene phosphonium salts. rn Das synthetische Konzept der vorliegenden Arbeit bestand in der Darstellung von Phosphonium-Salzen, deren molekularer Kationenradius durch gezielte chemische Modifikationen signifikant vergrößert werden konnte. Es gelang dabei erstmals monodisperse, hydrophobe Polyphenylen-Phosphoniumelektrolyte präparativ zugänglich zu machen auf Basis einer divergenten Synthesestrategie mittels thermaler, irreversibler [4+2] Diels-Alder Cycloaddition. Auch eine gezielte Oberflächenfunktionalisierung des Kations dieser neuartigen Phosphoniumsalze konnte durch den Einsatz von speziellen Wachstumsbausteinen (Derivaten des Tetraphenylcyclopentadienons) erreicht werden. Kristallstrukturanalysen, massenspektrometrische Untersuchungen sowie DOSY-NMR Messungen beweisen die erfolgreiche Umsetzung des synthetischen Konzepts.rnMittels dielektrischer Spektroskopie an einer Serie von Polyphenylen-Boratsalzen (zugänglich durch klassische Ionenmetathesereaktionen) wurde der Zusammenhang zwischen Dissoziationsgrad und Größe des ladungsneutralisierenden Kations untersucht. Es konnte festgestellt werden, dass die Größe der hier entwickelten Phosphoniumkationen in der Größenordnung der sogenannten Bjerrum-Länge liegt – eine lösungsmittelabhänige, charakteristische Größe für die Beschreibung von Ionendissoziationsgleichgewichten. Die dabei erhaltenen Leitfähigkeitswerte wurden analysiert und enthüllten den Zusammenhang zwischen elektrophoretischer Mobilität und Koordination zum jeweiligen Gegenion.rnAußerdem wurden im Rahmen dieser Arbeit neue Benzylphosphoniumsalze mit sterisch außerordentlich anspruchsvollen Polyphenylen-Substituenten in -Position dargestellt, welche unter Wittig-Bedingungen mit Aldehyden zu den entsprechenden Alkenen umgesetzt wurden. Hierbei konnte ein eindeutiger Zusammenhang zwischen erhöhter (Z)-Selektivität der entstandenen Olefine und der Größe des alpha-Substituenten des Phosphoniumsalzes erforscht werden. Ferner ließen sich sterisch gehinderte (Z)-Stilbene in guten Ausbeuten darstellen durch den Einsatz der hier entwickelten Wittig-Vorstufen. Abschließend konnten erste Experimente zur Darstellung hydrophobisierter Polyelektrolyte erfolgreich durchgeführt und ausgewertet werden. rn
DDC:	540 Chemie 540 Chemistry and allied sciences
Institution:	Johannes Gutenberg-Universität Mainz
Department:	FB 09 Chemie, Pharmazie u. Geowissensch.
Place:	Mainz
ROR:	https://ror.org/023b0x485
DOI:	http://doi.org/10.25358/openscience-1810
URN:	urn:nbn:de:hebis:77-40166
Version:	Original work
Publication type:	Dissertation
License:	In Copyright
Information on rights of use:	https://rightsstatements.org/vocab/InC/1.0/
Appears in collections:	JGU-Publikationen