Dissertation (PhD)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: This study comprises the preparation and characterisation of various novel
organometallic species of gold(I) by employing a range of anionic group 6 metal
Fischer-type carbene complexes and group 6 metal-acyl complexes as synthons of the
organic moieties introduced to the gold(I) electrophiles. The main objectives of this
work are to develop the use of Fischer-type carbene complexes as synthons in the
preparation of novel organometallic species along unusual reaction pathways and, in
doing so, to expand the organometallic chemistry of gold(I), especially Au-C bond
formation reactions.
By reacting various β-CH acidic Fischer-type alkoxy/dialkylamino/
alkthio(methyl)carbene complexes, first with a base, and then with a gold(I)
electrophile (Ph3PAu+), easy access to vinyl ether/dialkylamine/thioether complexes
of gold(I) coordinated to M(CO)5 (M = Cr, Mo, W) fragments, is obtained. When
methyl alkoxy- or dialkylaminocarbene complexes are employed, coordination of the
novel alkoxyvinyl-gold(I)PPh3 and dialkylaminovinyl-gold(I)PPh3 species to the
M(CO)5 fragments occurs in an asymmetrical fashion through the vinyl functionalities
of the novel gold(I) species. This usually unstable coordination mode for vinyl ethers
is stabilised by delocalisation of partial positive charges from the α-gold vinyl carbon
atoms to either the gold(I)PPh3 fragment [for η2-{alkoxyvinyl-gold(I)PPh3}M(CO)5
complexes] or the nitogen atoms of the vinyl amine group [for η2-{dialkylaminovinylgold(
I)PPh3}M(CO)5 complexes]. In the latter complexes this delocalisation occurs to
such an extent that these complexes are best described as zwitterions. The
corresponding negative charges in the bimetallic complexes reside on the M(CO)5
fragments. As a representative example, uncoordinated ethoxyvinyl-gold(I)PPh3 was
isolated in high yield via a ligand replacement reaction with PPh3. When Fischer-type
alkthio(methyl)carbene complexes are employed in this conversion, novel sulphur
coordinated {alkthiovinyl-gold(I)PPh3}Cr(CO)5 complexes are formed.The reaction mechanism involved in these conversions is believed to be the gold(I)
analogue of the hydrolysis of Fischer-type carbene complexes. In this mechanism the
bimetallic η2-vinyl ether coordinated {alkoxyvinyl-gold(I)PPh3}M(CO)5 complexes
represent stabilised gold(I) analogues of postulated transition states in the hydrolytic
decomposition of Fischer-type alkoxycarbene complexes. The term aurolysis is
conceived to describe the conversion when Ph3PAu+ is employed as electrophile
instead of H+. The formation of the bimetallic η2-vinyl ether coordinated complexes
in the current conversion, furthermore, strongly supports the existence of similar
transition states in the hydrolytic decomposition of Fischer-type alkoxycarbene
complexes. This mechanism is also accepted for the formation of analogous
η2-{dialkylaminovinyl-gold(I)PPh3}M(CO)5 and {alkthiovinyl-gold(I)PPh3}-S
Cr(CO)5 complexes when β-CH deprotonated Fischer-type dialkylamino- and
alkthiocarbene complexes are employed in this reaction.
The reaction of anionic group 6 metal-acyl complexes and their nitrogen analogues,
N-deprotonated Fischer-type aminocarbene complexes, leads to the formation of
acylgold(I) and novel imidoylgold(I) complexes coordinated to M(CO)5 (M = Cr, W)
fragments. In the previous complexes poor stabilisation of the M(CO)5 fragments
allows halide anions to readily form ionic adducts with these groups. This
characteristic of these products provides a useful reaction pathway to the first example
of a free acylgold(I) complex, benzoyl-AuPPh3. Coordination of the imine nitrogen
atom to the M(CO)5 fragments in the analogous bimetallic imidoylgold(I)-M(CO)5
complexes is much stronger. These complexes are remarkably stable and could even
be effectively isolated by means of low temperature silica gel chromatography.
As a preliminary reaction mechanism for this conversion we propose a mechanism
that is closely related to the aurolysis mechanism described above. The only
difference is that, instead of formal reductive elimination of vinyl
ethers/amine/thioether complexes of gold(I) from the M(CO)5 fragments, acyl and
imidoyl complexes of gold(I) are produced in this step. Furthermore, the (Z)-
stereoisomers of the bimetallic imidoylgold(I)-M(CO)5 complexes generated in this
conversion are exclusively obtained.A second N-deprotonation-auration reaction sequence performed on suitable
examples of the bimetallic imidoylgold(I)-M(CO)5 complexes yields, as the only
isolable product, a novel triangular Au2Cr cluster complex, cis-{η2-(Ph3PAu)2}
PPh3Cr(CO)4. This complex is the isolobal equivalent for the unstable molecular
hydrogen complex, (η2-H2)PPh3Cr(CO)4, and exhibits the shortest known Au-Au
separation between two gold atoms in cluster complexes of the type Au2M.
Finally, two novel and vastly different molecular structures of closely related anionic
benzoylpentacarbonyl tungstates, one with Li+ as counterion and another in which
exactly half the Li+-cations have been replaced by protons, highlight the importance
of hydrogen bonding and ion-dipole interactions in determining the solid state
structure of such complexes. / AFRIKAANSE OPSOMMING: Hierdie studie behels die bereiding en karakterisering van verskeie nuwe
organometaalkomplekse van goud(I). Hierdie komplekse is berei deur gebruik te
maak van n wye reeks anioniese groep 6 metaal Fischer-tipe karbeenkomplekse
asook anioniese groep 6 metaal asielkomplekse as sintetiese ekwivalente vir die
organiese fragmente wat gedurende die sintese aan die goud atoom gebind word. Die
hoofdoel van hierdie studie is om die gebruik van Fischer-tipe karbeenkomplekse as
sintetiese voorgangers in die bereiding van nuwe organometaalverbindings te
ontwikkel en om sodoende ook die organometaalchemie van goud verder uit te bou.
Veral die ontwikkeling van nuwe sintetiese metodologieë vir die bereiding van Au-C
bindings is hier van belang.
Verskeie Fischer-tipe alkoksie-/dialkielamino-/alktio-(metiel)karbeenkomplekse met
suuragtige waterstofatome geleë op die β-metallo-koolstofatoom is eers
onomkeerbaar gedeprotoneer. Byvoeging van die goud(I) elektrofiel, Ph3PAu+, lei -
volgens n ongewone reaksiemeganisme - tot die vorming van onderskeie vinieleter-,
dialkielvinielamien- en vinieltioeterkomplekse van goud(I). Hierdie komplekse is
verder ook op verskillende wyses aan M(CO)5 fragmente (M = Cr, Mo, W)
gekoördineer.
Die vinieleter- en vinielamienkomplekse van goud(I), wat vorm wanneer alkoksie- en
dialkielaminokarbeenkomplekse onderskeidelik in hierdie sintese aangewend word,
koördineer onsimmetries deur hulle viniel dubbelbindings aan die vrygestelde
M(CO)5-groepe. Hierdie normaalweg onstabiele vorm van vinieleterkoördinasie,
word gestabiliseer deur delokalisering van positiewe lading vanaf die α-goud viniel
koolstofatoom na die AuPPh3-fragment [vir die η2-{alkoksievinielgoud(
I)PPh3}M(CO)5 komplekse] óf na die stikstofatoom van die dialkielvinielamien
groep [vir die η2-{dialkielaminoviniel-goud(I)PPh3}M(CO)5 komplekse].
Laasgenoemde komplekse kan as zwitterione beskryf word. Die onderskeie
negatiewe ladings in hierdie komplekse bevind hulle hoofsaaklik op die M(CO)5
groepe. Sterk koördinerende ligande (bv. PPh3) verplaas die onsimmetriese viniel eter
vanaf die M(CO)5-fragment. Só kon, as n voorbeeld, die vrye etoksievinielgoud(
I)PPh3-kompleks met n hoë opbrengs berei word. Wanneer β-gedeprotoneerdeFischer-tipe tiokarbeenkomplekse met Ph3PAu+ reageer, vorm swawel
gekoördineerde {tioviniel-goud(I)PPh3}Cr(CO)5 bimetalliese komplekse in stede van
die π-komplekse.
Dit word voorgestel dat in die bogenoemde reaksies die goud(I)elektrofiel dieselfde
rol vervul as die proton gedurende die hidrolise van Fischer-tipe
alkoksiekarbeenkomplekse. Die bimetalliese, η2-vinieleter-gekoördineerde
{alkoksieviniel-goud(I)PPh3}M(CO)5-komplekse hier berei verteenwoordig dus
stabiele goud(I) analoë van voorgestelde tusseprodukte in so ’n meganisme. Die term
aurolise word voorgestel om die geval waar Ph3PAu+ in stede van H+ as elektrofiel
aangewend word te beskryf. Die vorming van bimetalliese, η2-vinieletergeko
ördineerde komplekse in die huidige reaksie ondersteun die moontlike vorming
van die voorgestelde tussenprodukte tydens die hidrolise van Fischer-tipe
alkoksie(metiel)karbeenkomplekse. ’n Soortgelyke meganisme kan ook gebruik word
om die vorming van die η2-{dialkiellamienviniel-goud(I)PPh3}M(CO)5- en
{alktioviniel-goud(I)PPh3}-S Cr(CO)5-komplekse vanuit β-CH gedeprotoneerde
Fischer-tipe dialkielamino- en tiokarbeenkomplekse en Ph3PAuCl te interpreteer.
Die reaksie van anioniese groep 6 oorgangsmetaal metaal-asielkomplekse en hulle
stikstofanaloë, N-gedeprotoneerde Fischer-tipe aminokarbeenkomplekse, lewer
onderskeidelik asiel- en imidoielkomplekse van goud(I) wat aan M(CO)5 fragmente
(M = Cr, W) koördineer. Die goud(I)asiel-M(CO)5 koördinasie deur die asielsuurstofatoom
is baie swak en die M(CO)5-eenheid in hierdie komplekse word maklik
deur haliedanione en sekere oplosmiddel molekules verplaas. Die haliedanione vorm
anioniese addukte met the M(CO)5 fragmente. Hierdie eienskap van die bimetalliese
komplekse verskaf sodoende n gerieflike sintetiese roete na die eerste voorbeeld van
n vrye asielgoud(I)-kompleks, bensoiel-AuPPh3. Koördinasie van die
imienstikstofatoom aan M(CO)5-groepe in die bg. imidoielkomplekse is egter veel
sterker. Die bimetalliese {imidoielgoud(I)}M(CO)5-komplekse is verbasend stabiel en
kan selfs effektief deur middel van lae temperatuur SiO2-kolomkromatografie
geïsoleer word. n Soortgelyke reaksie meganisme as wat voorgestel word vir die aurolise van
Fischer-tipe karbeenkomplekse word voorgestel vir hierdie reaksie. Die enigste
verskil is dat die formele reduktiewe eliminasie van n viniel-eter, -amien of -tioeter
vervang word met die vorming van asiel- of imidoielkomplekse van goud(I). Verder
word die (Z)-isomere van die bimetalliese {imidoielgoud(I)}M(CO)5-komplekse
uitsluitlik in hierdie reaksie verkry.
Wanneer geskikte voorbeelde van bimetalliese {imidoielgoud(I)}M(CO)5-komplekse
n tweede keer gedeprotoneer word en gereageer word met Ph3PAuCl, is die enigste
isoleerbare produk van die reaksie n driehoekige Au2Cr troskompleks, nl. cis-{η2-
(Ph3PAu)2}PPh3Cr(CO)4. Hierdie verbinding dien as n isolobale model vir die
onstabiele molekulêre waterstof kompleks , (η2-H2)PPh3Cr(CO)4, en besit verder die
kortste Au-Au afstand tussen twee goud atome in driehoekige troskomplekse wat nog
tot dusvêr gerapporteer is.
Laastens is die kristalstrukture van twee nou verwante anioniese {bensoiel}W(CO)5-
komplekse bepaal. Die enigste verskil tussen die hierdie twee verbindings is dat die
een slegs Li+ as teenioon bevat terwyl presies die helfte van die Li+-teenione in die
tweede struktuur deur protone verplaas is. Hierdie klein verskil in samestelling
veroorsaak egter drastiese verskille in die kristalstrukture van hierdie verbindings. Die
belangrikheid van waterstof bindings en ioon-dipool interaksies in die bepaling van
die vastetoestandstrukture van sulke verbindings word hierdeur beklemtoon.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/16046 |
| Date | 04 1900 |
| Creators | Esterhuysen, Matthias Wilhelm |
| Contributors | Raubenheimer, H.G., University of Stellenbosch. Faculty of Science. Dept. of Chemistry and Polymer science |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | xvii, 189 leaves :ill. |
| Rights | University of Stellenbosch |
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