Full Text Available
Note: Clicking the button above will open the full text document at the original institutional repository in a new window.
Heteroaryl carbene complexes : synthesis, reactivity and redox behaviour
Thesis (PhD)--University of Pretoria, 2013.
Saved in:
| Other Authors: | |
|---|---|
| Format: | Thesis |
| Language: | English |
| Published: |
University of Pretoria
2014
|
| Subjects: | |
| Tags: |
No Tags, Be the first to tag this record!
|
| _version_ | 1867613577222815744 |
|---|---|
| access_status_str | Open Access |
| author2 | Bezuidenhout, Daniela Ina |
| author_browse | Bezuidenhout, Daniela Ina |
| author_facet | Bezuidenhout, Daniela Ina |
| collection | Thesis |
| dc_rights_str_mv | © 2013 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. |
| description | Thesis (PhD)--University of Pretoria, 2013. |
| format | Thesis |
| id | oai:repository.up.ac.za:2263/40242 |
| institution | University of Pretoria (South Africa) |
| language | English |
| last_indexed | 2026-06-10T12:38:21.509Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UPSpace — University of Pretoria Institutional Repository |
| publishDate | 2014 |
| publishDateRange | 2014 |
| publishDateSort | 2014 |
| publisher | University of Pretoria |
| publisherStr | University of Pretoria |
| record_format | dspace |
| source_str | UPSpace — University of Pretoria Institutional Repository |
| spelling | oai:repository.up.ac.za:2263/40242 Heteroaryl carbene complexes : synthesis, reactivity and redox behaviour Bezuidenhout, Daniela Ina Van der Westhuizen, Belinda Fischer mono Biscarbene complexes Cyclic voltammetry Spectroelectrochemistry Reactivity Redox behaviour UCTD Thesis (PhD)--University of Pretoria, 2013. A series of Fischer mono- and biscarbene complexes of the type [MLn{C=(XR)R'}] was synthesized and characterized. The redox behavior of the complexes was studied by different techniques, including cyclic voltammetry, spectroelectrochemistry, ESR and computational methods. Different transition metals (M) and carbene substituents (XR, R') were employed to compare both the effect of the central metal atom as well as the carbene substituent. Thienyl, furyl and ferrocenyl chromium(0) mono- and biscarbene complexes with ethoxy and amino substituents were electrochemically studied in CH2Cl2. Results were mutually consistent with computational data showing that the carbene double bond of all complexes is reduced pseudo reversibly to an anion radical, -Cr-C•. The Cr centers are oxidized in two successive one electron transfer steps to Cr(II) via the Cr(I) intermediate. For all ferrocenyl carbene complexes the Fe(II) is oxidized after the first oxidation of Cr. It was found that with respect to the aryl substituents the donating effect decreases from Fc>Fu>Th. Stabilization from the XR substituent, where XR = NHR, also resulted in lower redox potentials compared to their OEt analogues. The inclusion of ferrocene in the carbene substituent was done, as its redox activity and increased donating effect are well known. Mono- and biscarbene complexes with ethoxy and amino substituents of both chromium and tungsten were electrochemically studied. Again experimental data were supported by computational studies. Similar to the ethoxy chromium complexes, reduction of the W=C fragment to -W-C• was observed. However oxidation of the Fc group occurred first before the electrochemically irreversible oxidation process for W(0) involving a three electron-mediated process as seen in chronocoulometric analyses. The tungsten oxidation was restricted to a W0/II, consistent with computational studies, by the use of the electrolyte [NnBu4][B(C6F5)4]. The short-lived W(II) species were calculated to be stabilized by agostic CH···W interactions, similar to the chromium analogues. To extend linkers between the metal-carbene termini and investigate metal-metal interaction, biferrocenyl and 2,5-thienylbiferrocenyl tungsten(0) mono-and biscarbene complexes were synthesized and studied by spectroelectrochemistry. A metal-metal charge transfer transition between the tungsten carbonyl increment and the biferrocenyl / 2,5-thienylbiferrocenyl unit was confirmed by infrared spectroelectrochemical studies. The electronic interaction in the corresponding cationic species can be described as weakly coupled class II systems according to Robin and Day. The cymantrenyl moiety, Mn(η5-C5H4)(CO)3, provides an interesting alternative to ferrocene as an organometallic molecular tag, however the instability of the radical cation impairs its use. Improved stability of the cation, monitored by electrochemical measurements, was accomplished by substituting a carbonyl with a ferrocenyl Fischer carbene ligand resulting in Mn(I) oxidation occuring at lower potentials than ferrocenyl oxidation. These uncommon Fischer carbene complexes is the first organometallic multi-tags reported. The mono cationic species, [CpMn(CO)2{=C(OEt)Fc}][PF6], could be isolated and characterized with ESR analysis. Finally, transmetallation from the tungsten(0) Fischer carbene complexes yielded examples of rare acyclic alkoxy- and aminocarbene complexes of gold(I). Single x-ray structures for all complexes could be obtained including the novel ferrocenophane dinuclear biscarbene Au(I) complex. All structures display unsupported aurophilic interactions, while the bridging biscarbene shows a semi-supported Au-Au interaction. In the case of the furanyl/thienyl methoxy monocarbene complexes, extended Au-Au interactions result in oligomeric structures. Although this study is of a fundamental nature, it is imperative for the understanding and design of gold compounds with specific applications. gm2014 Chemistry unrestricted 2014-06-17T13:05:24Z 2014-06-17T13:05:24Z 2014-04-23 2013 Thesis Van der Westhuizen, B 2013, Heteroaryl carbene complexes: synthesis, reactivity and redox behaviour, PhD thesis, University of Pretoria, Pretoria, viewed yymmdd <http://hdl.handle.net/2263/40242> D14/4/125/gm http://hdl.handle.net/2263/40242 en © 2013 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. application/pdf University of Pretoria |
| spellingShingle | Fischer mono Biscarbene complexes Cyclic voltammetry Spectroelectrochemistry Reactivity Redox behaviour UCTD Heteroaryl carbene complexes : synthesis, reactivity and redox behaviour |
| title | Heteroaryl carbene complexes : synthesis, reactivity and redox behaviour |
| title_full | Heteroaryl carbene complexes : synthesis, reactivity and redox behaviour |
| title_fullStr | Heteroaryl carbene complexes : synthesis, reactivity and redox behaviour |
| title_full_unstemmed | Heteroaryl carbene complexes : synthesis, reactivity and redox behaviour |
| title_short | Heteroaryl carbene complexes : synthesis, reactivity and redox behaviour |
| title_sort | heteroaryl carbene complexes synthesis reactivity and redox behaviour |
| topic | Fischer mono Biscarbene complexes Cyclic voltammetry Spectroelectrochemistry Reactivity Redox behaviour UCTD |
| url | http://hdl.handle.net/2263/40242 |