N-heterosikliese karbeenkomplekse van groep 10 metale : nuwe moontlikhede

Kruger, Anneke (2007-03)

Thesis (MSc)--University of Stellenbosch, 2007.

Thesis

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.

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