Thesis (MSc)--University of Stellenbosch, 2007. / ENGLISH ABSTRACT: This study comprises the synthesis and characterisation of N-heterocyclic carbene complexes
of group 10 metals with the main focus on such complexes with the nucleophilic N-atom in a
position further than the α-position from the carbene carbon atom. These compounds were
synthesised by the initial alkylation of quinoline- and acridine derivatives followed by the
oxidative addition of the resulting salts to the complexes M(PPh3)4 (M = Ni, Pd, Pt). To
complete the study an investigation of the catalytic activity and stability of such compounds
in C,C-coupling catalysis was conducted.
The carbene ligands used differed with respect to the position of the N-atom relative to the
carbene carbon atom as well as with respect to substituents. The oxidative addition of the
quinolinium- and acridiniumchloride salts to Ni(PPh3)4 was initially problematic. The desired
product formed only in small amounts and could not be isolated easily. However, by replacing
toluene with more polar THF as solvent, the nickel complexes could be synthesised in high
yield without any indication of decomposition. Oxidative addition to Pt(PPh3)4 also yielded
the desired product, although a number of by-products were formed as well. The molecular
structure of trans-chloro(1,3-dimethyl-1,2-dihydroquinoline-2-ylidene)-bis(triphenylphosphine)
platinum(II) trifluoromethanesulfonate could nevertheless be determined by X-ray
crystallography.
The new one-N, six membered, heterocyclic carbene complexes were all unambiguously
characterised by NMR spectroscopy, mass spectrometry and X-ray crystallography. The
carbene character of the complexes was corroborated by a large downfield chemical shift (δ
203 – 230) of the carbene carbon atoms in their 13C NMR spectra. The analyses furthermore
indicated that with the exception of cis-chloro(1-methyl-3-phenyl-1,4-dihydroquinoline-4-
ylidene)bis(triphenylphosphine)palladium(II) hexafluorophosphate, all the palladium, nickel
and platinum complexes exhibit a trans arrangement of the PPh3 ligands. Both the cis- and the
trans isomers of the complexes, chloro(1,3-dimethyl-1,2-dihydroquinoline-2-ylidene)-
bis(triphenylphosphine)palladium(II) tetrafluoroborate and chloro-(1,3-dimethyl-1,2-dihydroquinoline-
2-ylidene)bis(triphenylphosphine)palladium(II) trifluoromethanesulphonate are,
however, present in solution. The molecular structure of both isomers were determined by Xray
crystallography. Crystallographic studies revealed that the new family of cationic
complexes exist in a slightly distorted square planar environment with the carbene ligand orientated almost perpendicular to this plane. The metal-carbene bond lengths are insensitive
to variations in the substituents on the carbene ligands and are therefore not a suitable
parameter to distinguish between the strengths of these bonds.
The N-heterocyclic carbene ligands with the N-atom removed from the carbene carbon atom
by three bonds, exhibit a greater trans influence in the palladium complexes than those with
the N-atom in the α-position. This is an indication of the better σ-donor ability of the former.
A significant difference in the Ni-Cl bond lengths could, however, not be detected.
The catalytic activity of the new synthesised palladium and nickel complexes in the Mizoroki-
Heck and Suzuki-Miyaura coupling reactions, were investigated. The palladium complexes
tested show potential as precatalysts for the Mizoroki-Heck reaction, although relatively high
temperatures were needed to effect coupling, while coupling of aryl chlorides did not occur at
all. The trans-chloro(1,2-dimethyl-1,4-dihydroquinoline-4-ylidene)bis(triphenylphosphine)-
palladium(II) trifluoromethanesulphonate complex also displayed high activity in the C,Ccoupling
of bromofluorene with arylboronic acids in the Suzuki-Miyaura coupling reaction. It
even yielded high conversions in instances where sterically hindered aryl halides were used.
The trans-chloro(1,2-dimethyl-1,4-dihydroquinoline-4-ylidene)bis(triphenylphosphine)-
nickel(II) trifluoromethanesulphonate complex catalyses the coupling of sterically hindered
arylbromides as well as arylchlorides to arylboronic acids. By further optimising the reaction
conditions and increasing the streric bulk of the carbene ligands, even better results in both
the Mizoroki-Heck and the Suzuki-Miyaura reactions are expected. / AFRIKAANSE OPSOMMING: Hierdie studie behels die sintese en karakterisering van N-heterosikliese karbeenkomplekse
van groep 10 metale. Daar is veral gefokus op N-heterosikliese karbeenligande waarin die
nukleofiele N-atoom verder as die α-posisie vanaf van die karbeenkoolstofatoom verwyder is.
Die betrokke komplekse is gesintetiseer deur die alkilering van kinolien- en akridienderivate,
gevolg deur die oksidatiewe addisie van die resulterende soute aan die komplekse M(PPh3)4
(M = Ni, Pd, Pt). Om die studie af te rond is die katalitiese aktiwiteit van dié komplekse in
C,C-koppelingsreaksies ondersoek.
Karbeenligande wat slegs een nukleofiele stikstofatoom besit en verskil ten opsigte van die
posisie van dié atoom relatief tot die karbeenkoolstofatoom asook substituente aan die ligand,
is gebruik. Die oksidatiewe addisie van die kinoliniumchloried- en akridiniumchloriedsoute
aan Ni(PPh3)4 het aanvanklik probleme opgelewer, sodat slegs ’n klein hoeveelheid van die
verlangde produk, wat moeilik isoleerbaar was, gevorm het. Deur egter ’n meer polêre
oplosmiddel, THF, in plaas van tolueen te gebruik, kon die nikkelkomplekse met goeie
opbrengs en sonder enige aanduiding van ontbinding, berei word. Oksidatiewe addisie aan
Pt(PPh3)4 het die verlangde produk gelewer, alhoewel ’n aantal neweprodukte ook gevorm
het. Ten spyte hiervan is daarin geslaag om die molekulêre struktuur van trans-chloro(1,3-
dimetiel-1,2-dihidrokinolien-2-ilideen)bis(trifenielfosfien)platinum(II) trifluorometaansulfonaat
kristallografies te bepaal.
Die nuwe gesintetiseerde een-N, seslid, heterosikliese karbeenkomplekse is deur KMRspektroskopie,
massaspektrometrie en X-straalkristallografie eenduidig gekarakteriseer. Die
karbeenkarakter van die komplekse is bevestig deur die ver veldafwaartse chemiese
verskuiwing (δ 203 - 230) van die karbeenkoolstofatoom in die 13C-KMR-spektra. Die
analises toon ook dat, met die uitsondering van cis-chloro(1-metiel-3-feniel-1,4-
dihidrokinolien-4-ilideen)bis(trifenielfosfien)palladium(II) heksafluorofosfaat, al die
palladium-, nikkel- en platinumkomplekse ’n trans-rangskikking van die PPh3-ligande besit.
Die cis- sowel as die trans-isomere van die palladiumkomplekse chloro(1,3-dimetiel-1,2-
dihidrokinolien-2-ilideen)bis(trifenielfosfien)palladium(II) tetrafluoroboraat en chloro(1,3-
dimetiel-1,2-dihidrokinolien-2-ilideen)bis(trifenielfosfien)palladium(II) trifluorometaansulfonaat,
is in oplossing teenwoordig en die molekulêre struktuur van albei isomere is
kristallografies bepaal. Dit is vasgestel dat al die kationiese komplekse in ’n effens verwronge vierkantvlakomgewing, met die karbeenligand byna loodreg op dié vlak, voorkom. Die
metaal-karbeenbindingslengtes is onsensitief teenoor ’n variasie in die substituente gebind aan
die karbeenligande en dit is nie ’n handige parameter om tussen die sterktes van dié bindings
te differensieer nie.
Die N-heterosikliese karbeenligande waarvan die N-atoom in ’n posisie drie bindings van die
karbeenkoolstofatoom af voorkom, toon ’n effens sterker trans-invloed as die ligande met ’n
α-stikstofatoom in die palladiumkomplekse. Dit is ’n aanduiding dat eersgenoemde ligande
beter σ-donor eienskappe besit. Die nikkelkomplekse verskil egter nie betekenisvol ten
opsigte van hul Ni-Cl bindingslengtes nie.
Die katalitiese aktiwiteit en stabiliteit van die nuwe reekse palladium- en nikkelkomplekse is
in Mizoroki-Heck en Suzuki-Miyaura-koppelingsreaksies ondersoek. Ofskoon relatief hoë
temperature nodig is om koppeling te bewerkstellig en die komplekse nie koppeling van ’n
arielchloried met butielakrilaat kataliseer nie, toon die palladiumkomplekse tóg potensiaal as
prekatalisatore in die Mizoroki-Heck-reaksie. Die kompleks, trans-chloro(1,2-dimetiel-1,4-
dihidrokinolien-4-ilideen)bis(trifenielfosfien)paladium(II) trifluorometaansulfonaat, toon ook
uitstekende katalitiese aktiwiteit in die C,C-koppeling van bromofluoreen met arielboorsure in
die Suzuki-Miyaura-koppelingsreaksie. Hierdie kompleks kataliseer selfs die koppeling van
steries gehinderde arielhaliede met arielboorsure. Die kompleks trans-chloro(1,2-dimetiel-
1,4-dihidrokinolien-4-ilideen)bis(trifenielfosfien)nikkel(II) trifluorometaansulfonaat,
bemiddel koppeling van arielbromied-, sowel as steries gehinderde arielchloriedsubstrate aan
arielboorsure. Selfs beter resultate in die Mizoroki-Heck- sowel as die Suzuki-Miyaurakoppelingsreaksies
word verwag deur verdere optimalisering van die reaksiekondisies en die
inbouing van groter steriese hindering in die ligande.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/19636 |
| Date | 03 1900 |
| Creators | Kruger, Anneke |
| Contributors | Raubenheimer, H.G., Cronje, S., Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | Afrikaans |
| Detected Language | English |
| Type | Thesis |
| Format | xvi, 115 leaves : ill. |
| Rights | Stellenbosch University |
Page generated in 0.3016 seconds