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Thesis (PhD (Chemistry and Polymer Science))--Stellenbosch University, 2008. / Alkylated acetonitrile that forms during the synthesis of the sulfonium salt, [(Me3)2(MeS)S][BF4], is involved in the formation of new , -unsaturated Fischer-type carbene complexes from (CO)5M=C(OMe)CH2Li (M = Cr, W). Metal migration observed when the substitution product obtained from the reaction of the anionic carbene complexes (CO)5M=C(NMe2)CºC¯ (M = Cr, W) with Ph3PAu+ was left in solution, was also kinetically and theoretically investigated. 1H NMR and quantum mechanical (at the B3LYP level of theory) data indicated a complicated mechanism. The a,b-unsaturated Fischer-type carbene complex, (CO)5Cr=C(OMe)CH=C(Me)NH(Me), obtained from the reaction of (CO)5M=C(OMe)CH2¯ with alkylated acetonitrile, was transformed into the new remote one-N, six-membered, carbene ligand (rN1HC6) complex, (CO)5Cr=C(CH=C(Me)N(Me)CH=C(nBu). The carbene ligand unprecedentedly preferred the softer Rh(CO)2Cl moiety to the Cr(CO)5 metal fragment and transferred readily. A new series of remote and abnormal square planar compounds [r/a(NHC)(PPh3)2MCl]CF3SO3 (M = Pd or Ni) was prepared by oxidative substitution. The various positions for metal-carbon bond formation on a pyridine ring to furnish various ligand types i.e. C2 for nN1HC6, C3 for aN1HC6 or C4 for rN1HC6 received attention. The ligands were arranged in increasing order of carbene character, aNHC < nNHC < rNHC and trans influence, nN2HC5 ~ aN1HC6 ~ nN1HC6 < rN1HC6. In competitive situations, oxidative substitution occurred selectively at C4 of the pyridine ring rather than at C2 and on the aromatic ring containing the heteroatom (C4), rather than on an annealed aromatic ring (C7). Crystal and molecular structure determinations confirmed the preferred coordination sites. Quantum mechanical calculations (at the RI-BP86/SV level of theory) indicated that the chosen carbene ligand has a much larger influence than the metal on the BDE of the M-Ccarbene bond; the farther away the N-atom is from the carbene carbon, the stronger the bond. In complexes that also contain additional external nitrogen atoms, e.g. trans-chloro(N-methyl-1,2,4- trihydro-2-dimethylaminepyrid-4-ylidene)bis(triphenylphosphine)palladium(II) triflate and transchloro( N-methyl-1,2,4-trihydro-2-dimethylaminepyrid-4-ylidene)bis(triphenylphosphine)nickel(II) triflate, stabilisation originates from both the nitrogens. 2-Chloro-1-methyl-1H-pyrid-4-ylidenephenylammonium triflate afforded complexes with both remote as well as normal nitrogen atoms. New azole complexes of palladium and nickel with remote heteroatoms were also prepared from N-methyl-4',4'-dimethyl-2'-thiophen-3-chloro-2-yl-4,5-dihydro-oxazole. Employing the compound 1,5-dichloroanthraquinone, the product of a double oxidative substitution on two Pd centra could be isolated but not alkylated. The fact that the chemical shift of the metal bonded carbon in the 13C NMR spectrum can not be used as absolute measure of carbene character, was emphasised in a compound where the heteroatom was situated seven bonds away from the carbon donor. In efforts to synthesise a sulphur-bridged complex that contains carbene ligands, crystals of transdi- iodobis(1,3-dimethyl-imidazoline-2-ylidene)palladium were obtained. Bridged thiolato complexes with N1HC6 ligands were unexpectedly found in the attempt to substitute the halogen on chosen square planar carbene complexes of palladium, widening the application possibilities of N1HC6 ligands in organometallic chemistry beyond that of catalysis. A trinuclear cluster, [(PdPPh3)3(μ-SMe)3]BF4 was isolated as a by-product of these reactions. A series normal and abnormal thiazolylidene complexes of nickel and palladium were prepared by oxidative substitution of the respective 2-, 4- and 5-bromothiazolium salts with M(PPh3)4 (M = Pd or Ni), and unequivocally characterised. In a preliminary catalytic investigation, all the thiazolinium and simple pyridinium derived palladium complexes showed activity in the Suzuki-Miyaura coupling reaction. Little variation in activity in the order a (N next to carbon donor) > n > a (S next to carbon donor) was found for the former series, whereas decreased activity was exhibited in the sequence r > a > n of the latter group. The pyridinium derived complexes showed superior activity to the thiazolinium ones. The rNHC complex, trans-chloro(N-methyl-1,2,4-trihydro-2- dimethylaminepyrid-4-ylidene)bis(triphenylphosphine)palladium(II) triflate, showed similar Suzuki-Miyaura activity to the standard N2HC5 carbene complex precatalyst, trans-chloro[(1,3- dimethyl-imidazol-2-ylidene)triphenylphosphine]palladium(II) triflate.

Des carbènes N-hétérocycliques (NHC)s ont été employés comme catalyseurs organiques de la polymérisation par étapes du téréphtaldéhyde. Cette partie est une application en chimie des polymères de la réaction de « condensation de la benzoïne » catalysée par les NHCs impliquant un mono-aldéhyde analogue. Des poly(1,4-phénylène-1-oxo-2-hydroxyéthylène)s ou « polybenzoïnes » ont ainsi été obtenus par polymérisation en solution dans le DMSO ou le THF comme solvant à une température inférieure à 40 °C. La présence de chaines de polybenzoïne cycliques a pu être mise en évidence. La proportion de ces cycles dépend de la nature du catalyseur carbénique et de la polarité du milieu réactionnel. Dans la deuxième partie du travail, des solutions simples ont été proposées pour manipuler les NHCs de manière plus aisée, en évitant leur dégradation prématurée. Pour ce faire, des supports polymères porteurs de sites carbéniques, c’est à dire des « poly(NHC)s », ont été développés et employés à des fins d’organocatalyse. Bien que recyclables, ces « poly(NHC)s » restent assez sensibles aux traces d’impuretés. Un moyen de les protéger est de les faire réagir avec le CO2. Les adduits ainsi formés, « poly(NHC-CO2)s », peuvent alors être employés comme précurseurs pour générer les « poly(NHC)s » in situ, par simple activation thermique, le retour aux « poly(NHC-CO2)s » pouvant être effectué par carboxylation des « poly(NHC)s ». Enfin, des méthodes de synthèse de composés de type imidazolium (version moléculaire) et polyimidazolium (version polymère supportée) à contre anion hydrogénocarbonate (HCO3-) ont été développées. De tels précurseurs peuvent eux-mêmes servir de pré-catalyseurs (moléculaires ou polymères) pour générer, par chauffage, des NHCs et poly(NHC)s, offrant un moyen très pratique de mener des réactions d’organocatalyse et de recycler les catalyseurs. / N-Heterocyclic carbenes (NHCs) have been employed as organic catalysts for the step-growth polymerization of terephtaldehyde. This part is an application to polymer chemistry of the so-called “benzoin condensation”, reaction catalyzed by NHCs involving a mono-aldehyde substrate. Poly(1,4-phenylene-1-oxo-2-hydroxyethylene)s or « polybenzoins » have thus been obtained by polymerization reactions conducted in DMSO or THF at temperatures below 40°C. Presence of cyclic polybenzoins has been put forward. The content of such cyclic species was found to vary as a function of the NHC catalyst employed and of the reaction media used. In a second part, simple solutions have been proposed to easily handle NHCs, by avoiding their degradation. For this purpose, polymer supports bearing NHCs moities, i.e “poly(NHC)s”, have been developed and employed for the purpose of organocatalysis. Even if “poly(NHC)s” were found to be recyclable, they still remain sensitive to impurities. Another way to protect the carbenic centers is to react “poly(NHC)s” with CO2. The adducts thus obtained, “poly(NHC-CO2)s”, can then be employed as precursors for the in situ generation of “poly(NHC)s”, by a simple thermal activation. A further carboxylation of such generated species allow for the recovering of “poly(NHC-CO2)s”. Finally, synthetic methods for the preparation of imidazolium (molecular version) and polyimidazolium (supported polymer version) salts with hydrogenocarbonate (HCO3-) as counter-anion have been developed. Such precursors can serve as precatalysts (molecular or supported) to generate, by heating, NHCs and poly(NHC)s, giving a practice way to conduct organocalysed reactions and recycle the catalysts.

En plus du site de coordination interne classique des porphyrines, il est possible de fonctionnaliser le macrocycle par des sit es de coordination externes. Ce travail de thèse porte sur la fonctionnalisation de deux carbones b-pyrroliques adjacents afin d'obtenir des porphyrines conjuguées avec des ligands de type carbène N-hétérocyclique (CNH).Les CNHs présentent de remarquables propriétés électroniques qui en font aujourd'hui des ligands incontournables en catalyse et en chimie organométallique. L'objectif de ce travail de thèse a été d'étudier l'influence de la porphyrine sur les propriétés électroniques du ligand périphérique CNH, et de moduler les propriétés électroniques et catalytiques de complexe métalliques en fonction des modifications chimiques apportées à la porphyrine, à savoir sa métallation ou la protonation des azotes de la porphyrine base-libre.Dans un premier temps, les différentes méthodes de synthèse développées afin d'obtenir différents sels d'imidazolium conjugués avec le macrocycle porphyrinique sont développées. Ces sels d'imidazolium sont les précurseurs des ligands porphyrine-CNH. Afin d'étudier les propriétés catalytiques de complexes contenant des ligands de type porphyrine-CNH, plusieurs complexes de palladium(II) ont été synthétisés et caractérisés. Les études des propriétés catalytiques de ces complexes testées sur le couplage de Heck ont démontré que de bien meilleures activités catalytiques étaient observées si les porphyrines contiennent un cation métallique. Enfin, les propriétés des ligands CNH ont été étudiées sur des complexes de types (CNH)Rh(COD)X et (CNH)Rh(CO)2X avec X = I ou Cl. / In addition to the usual inner coordination site of porphyrins, it is possible to functionalize the macrocycle by external coordination sites. This PhD thesis is devoted to the functionalization of two neighboring b-pyrrolic carbons in order to obtain porphyrins fused to peripheral N-heterocyclic carbene ligands (NHC).NHC ligands are known to display outstanding electronic properties which render them important ligands in the fields of catalysis and organometallic chemistry. The aim of this PhD work was to study the influence of the porphyrin on the electronic properties of the peripheral NHC ligand, and to modulate the electronic and catalytic properties of anchored metal complexes according to the chemical modifications brought to the porphyrin, ie. its metallation or the protonation of the free-base porphyrin.Firstly, the different synthetic procedures to obtain porphyrins fused to imidazolium rings were developed. These imidazolium salts are the key precursors of the porphyrin-NHC ligands. In order to study the catalytic properties of metal complexes containing porphyrin-NHC ligands, several palladium(II) complexes were synthesized and characterized. The study of the catalystic properties of these complexes showed that better catalytic activities were observed if the porphyrins contain a metal cation. Then, the electronic properties of these NHC ligands were evaluated for (NHC)Rh(COD)X and (NHC)Rh(CO)2X complexes with X = I or Cl.

Fabrication of surfaces with versatile functional groups is an important research area. Hence, it is essential to control and tune the surface properties in a reliable manner. Vinyl-terminated self-assembled monolayers (SAMs) offer significant flexibility for further chemical modification and can serve as a versatile starting point for tailoring of surface properties. Here a synthetic route for the preparation of vinyl-terminated trichlorosilane self-assembling molecules: 9-decenyltrichlorosilane (CH₂=CH-(CH₂)₈-SiCl₃), 10-undecenyltrichlorosilane (CH₂=CH-(CH₂)₉-SiCl₃), and 14-pentadecenyltrichlorosilane (CH₂=CH-(CH₂)₁₃-SiCl₃) is presented. These molecules were used for the preparation of SAMs in either liquid or vapour phase processes. Commercially available methyl-terminated self-assembling molecules: decyltrichlorosilane (CH₃-(CH₂)₉-SiCl₃) and octadecanetrichlorosilane (CH₃-(CH₂)₁₇-SiCl₃) were used as controls. The resultant films were characterised by X-ray photoelectron spectroscopy (XPS), contact angle analysis, ellipsometry, and atomic force microscopy (AFM). Well defined, vinyl-terminated SAMs were further chemically modified with carbenes (:CCl₂, :CBr₂, :CF₂) and hexafluoroacetone azine (HFAA). The reactions were performed in the liquid or the vapour phase. The resulting SAMs were characterised using the same methods as for the vinyl-terminated monolayers. Successful modification was confirmed by the appearance of new signals in the XPS spectrum, with simultaneous changes in water contact angle values and unchanged thickness values. Methyl-terminated SAMs were also exposed to carbenes and HFAA as a control system. These are the first examples of C-C bond formation on SAMs in the vapour phase.

This thesis describes our physical organic and mechanistic investigations into N Heterocyclic Carbene (NHC) mediated organocatalytic transformations, through a collaboration with the research group of Dr AnnMarie O'Donoghue and PhD student Richard Massey at Durham University. Initial research focused upon the determination of kinetic acidities and associated pKₐ values for a range of triazolium salts using C(3) H/D exchange, monitored by ¹H NMR spectroscopy. Estimates for pKₐ values in the range 16.6 17.4 were obtained, which are some ~2 and ~3 5 pK units lower than analogous imidazolium and thiazolium species respectively, with modest N substituent (0.3 pK units) effects observed. At lower pD values, an altered pD dependence indicates a dicationic triazolium species is formed (through N(1) protonation) with an estimated pKₐᴺ¹ of -0.2-0.5 and C(3) H pKₐ values at least 2 units lower than their monocationic analogues. This methodology was subsequently extended to mesoionic NHCs, where pKa values of 23.0 27.1 for a range of triazolium and 30.2 31.0 for a range of imidazolium salts were estimated. A detailed study of the NHC catalysed intramolecular Stetter reaction was also undertaken using ¹H NMR spectroscopy. A range of 3 (hydroxybenzyl)azolium salts (adducts), formed from the addition of NHC to aldehyde were isolated, enabling the generation of reaction profiles and the determination of rate constants. The reaction proceeds via rapid and reversible adduct generation, followed by rate limiting Breslow intermediate formation, with electron withdrawing N aryl substituents increasing the rate of product formation. Consistent with rate limiting deprotonation, deuterium exchange studies of O methylated adduct analogues found electron withdrawing N-aryl units gave faster exchange. Examination of the equilibrium constants for adduct formation revealed that both in the case of NHCs bearing 2,6 disubstituted N aryl units and aldehydes bearing a 2 ether substituent, the equilibrium position is significantly shifted towards adduct. Finally, studies at sub-stoichiometric NHC concentrations, monitored by HPLC, imply the reaction is first order with respect to NHC precursor, but zero order in aldehyde, again indicative of rate limiting deprotonation.

L’utilisation de carbènes N-hétérocycliques (NHCs), en tant qu’activateurs organiques « multitâches », a permis la polymérisation de deux classes de monomères : les monomères vinyliques de type (méth)acrylique et les monomères cycliques de type époxyde. En particulier, la polymérisation par transfert de groupe (GTP) catalysée par les NHCs a été utilisée pour polymériser les monomères acryliques et méthacryliques, dans des solvants polaires comme apolaires, en présence d’un amorceur de type acétal de cétène silylé. Sur cette base des copolymères à blocs « tout-acrylique » ont été synthétisés. Dans une autre étude, la polymérisation par ouverture de cycle (ROP) des oxydes d’éthylène et de propylène a été induite par les NHCs. Dans un premier cas, les NHCs ont été utilisés comme amorceurs de la réaction. Puis, en employant un amorceur tiers, ils ont servi de catalyseurs de la ROP. Des poly(oxyde d’éthylène) et poly(oxyde de propylène) hétérodifonctionnels ont été synthétisés. Enfin, une dernière approche a permis de concilier les deux méthodes de polymérisation. A l’aide d’un système unique d’amorçage, la copolymérisation séquentielle d’un monomère vinylique polaire et d’un monomère cyclique a pu être réalisée. / The use of N-heterocyclic carbenes (NHCs) as multitask organic activators has enabled the polymerization of two classes of monomers: polar vinylic monomers like (meth)acrylics, and cyclic epoxides. In particular, the NHC-catalyzed group transfer polymerization (GTP) has been used to polymerize both acrylic and methacrylic monomers, either in polar or apolar solvents, in the presence of a silyl ketene acetal as initiator. On this basis, “all-acrylic” block copolymers have been synthesized. In another study, the ring-opening polymerization (ROP) of ethylene and propylene oxides was induced by NHCs. In one case, NHCs have been used as initiators of the reaction. On the other hand, using a third compound, they have served as catalysts for the ROP. Heterobifonctional poly(ethylene oxide)s and poly(propylene oxide)s have been synthesized. A final approach has brought together the two polymerization methods. Using a single initiating system, the sequential copolymerization of a polar vinylic monomer and a cyclic monomer has been achieved.

Une série de calixarènes portant une unité imidazolium ou deux, en conformation cône ont été synthétisés et caractérisés par différentes méthodes. Ces sels chargés positivement constituaient des précurseurs de carbènes N-hétérocycliques pour la synthèse de complexes de nickel correspondants. Les complexes Ni-NHC-calix[4]arènes obtenus ont été testés dans la catalyse de la réaction de couplage croisé de Suzuki-Miyaura. Des moyennes à bonnes conversions ont été obtenues selon l’espacement du centre métallique de la cavité calixarénique, ainsi que le nombre de centre métallique présents sur la même plateforme. / A series of new calix[4]arenes bearing one or two imidazoliums units in the lower rim were synthesized as precursors of N-heterocyclic carbenes for the synthesis of the corresponding nickel complexes. All products obtained were characterized by NMR spectroscopy, microanalysis and mass spectroscopy and was revealed to be in cone conformation. The application of Ni-NHC-calix[4]arene in Suzuki-Miyaura cross coupling showed moderate to good conversions. This is been depending on the length of the alkyl chain and the number of the catalytic centers grafted on the platform.

Photokontrolle von Eigenschaften einzelner Moleküle und größerer Molekülvereinigungen ist ein faszinierendes Feld aktueller chemischer Forschung. Das schlichte Potential der genauen Adressierbarkeit von chemischer Reaktivität sowie die Möglichkeit durch Ausnutzen des katalytischen Zyklus einen Lichtstimulus in ein verstärktes chemisches Signal zu übersetzen, machen die Photokontrolle über katalytische Aktivität zu einem besonders attraktiven Ziel. Daher wurde im Rahmen dieser Dissertation ein allgemeines Konzept zur Realisierung von photoschaltbaren Katalysatoren entwickelt, das auf der reversiblen sterischen Abschirmung eines katalytisch aktiven Zentrums durch eine photochrome Abschirmungsgruppe beruht. Durch Vorgabe des Schaltzustandes des Photochromes kann die Aktivität des Katalysators bestimmt werden. Das Konzept wurde durch die Entwicklung von konformativ eingeschränkten, photoschaltbaren Piperidinbasen umgesetzt, die synthetisch leicht durch einen in hohem Maße modularen Zugang erhalten werden konnten. Die Piperidinbasen erlaubten die Photokontrolle der Katalysatoraktivität in der Nitroaldol-Reaktion (Henry-Reaktion). Durch die Optimierung der Substituenten konnten bemerkenswerte katalytische AN/AUS-Verhältnisse erreicht werden. Die Reaktivitätsunterschiede konnten mit Änderungen der Basizität in Abhängigkeit vom Schaltzustand korreliert werden. Systematische NMR-spektroskopische und theoretische Untersuchungen der strukturellen Dynamik des Katalysators in Lösung ermöglichten die Formulierung von detaillierten Struktur-Reaktivitäts-Beziehungen. Eine Erweiterung des Konzepts auf intrinsisch reaktivere Katalysatoren sollte zu einer verbesserten Anwendbarkeit beitragen. Daher wurde das Konzept der reversiblen sterischen Abschirmung auf katalytisch aktive N-heterozyklische Carbene übertragen. Eine erfolgreiche Synthese wurde durch ungünstige sterische Wechselwirkungen zwischen den abschirmenden Gruppen an den Stickstoffatomen des Carbens verhindert. / Photocontrol over properties of single molecules and assemblies thereof is an appealing area of current chemical research. The mere potential to selectively address chemical reactivity as well as the possibility to transform an incoming light stimulus into an amplified chemical signal by exploiting the associated catalytic cycle renders photocontrol of catalytic activity a particularly attractive goal. In this dissertation, a general concept for the realization of photoswitchable catalysts was developed, based on reversible steric shielding of a catalyst’s active site by a photochromic blocking group. Dictating the photochrome’s switching state enables gated access to the active site, thereby photocontrolling the catalyst’s chemical reactivity. The concept was realized by designing conformationally restricted, photoswitchable piperidine bases, which were easily synthesized exploiting a highly modular approach. Indeed, the developed piperidine bases allowed to photocontrol the catalysts’ activities in the nitroaldol reaction (Henry reaction) and by tuning of the substituents significant catalytic ON/OFF-ratios were achieved. The reactivity differences could be correlated with changes of basicity depending on the photochrome’s switching state. Systematic NMR-spectroscopic and computational studies of the catalysts’ structural dynamics in solution enabled the formulation of detailed structure-reactivity relationships. Strategies for the implementation of the concept of reversible steric shielding into the N-heterocyclic carbene (NHC) motif were devised to exploit the high reactivity of NHCs in numerous catalytic processes, which is expected to greatly enhance the utility of the concept. However, profound steric shielding of the active site to suppress unwanted OFF-state reactivity prevented the synthetic realization of the concept due to unfavorable steric interactions upon formation of the heterocyclic carbene from suitable precursors.

Ce mémoire est consacré à la synthèse et à l'étude de complexes métalliques originaux contenant des carbènes N-hétérocycliques (NHCs) fortement encombrés. Trois familles ont été élaborées : 1) des complexes Pd-PEPPSI "dissymmétriques" comportant un ligand imidazolylidène (Im) ayant comme N-substituants un groupe 9-alkyl-9-fluorényle (AF) ainsi qu'un aryle. Ces complexes se sont avérés des catalyseurs remarquables en couplage de Suzuki-Miyaura, présentant des performances comparables à celles d'analogues porteurs de deux groupes AF (dont l'excellente efficacité avait déjà été établie), démontrant ainsi le fort rôle stabilisateur du groupe AF; 2) des complexes trigonaux de cuivre(I) de formule générale [Cu(Im)(2,2'-dipyridylamine)]BF4 où le ligand carbénique est soit un carbène symétrique de type AF2-Im, soit dissymétrique de type (AF,Ar)-Im. Ici encore, la présence de substituants AF est un élément favorisant la stabilité des complexes en solution par rapport à une décomposition photo-induite. Contrairement à son anaolgue ayant un imidazolylidène porteur de deux substituants EtF, le complexe [Cu((EtF,Ph)-Im)(2,2'-dipyridylamine)]BF4 présente la particularité d'être luminescent en solution et à l'état solide; 3) des complexes Pd-PEPPSI contenant un imidazolilydène N-substitué par deux groupes identiques dont les extrémités sont des récépteurs potentiels de type calix[4]arène. Ces complexes ont la propriété de s'auto-assembler en formant une entité où les centres métalliques sont stériquement très protégés, avec pour conséquence de modifier sensiblement les propriétés catalytiques attendues du complexe. / Described herein are the stepwise syntheses and properties of three types of complexes based on sterically encumbered N-heterocyclic carbenes (NHCs): 1) Pd-PEPPSI complexes with an unsymmetrical imidalolylidene ligand having its N atoms substituted by a bulky 9-alkyl-9-fluorenyl (AF) group and an aryl group. These turned out to be very active Suzuki-Miyaura cross coupling catalysts with an activity comparable to previously reported, highly performing "symmetrical" analogues which bear two identical AF substituents. These findings illustrate the high stabilising effect of each individual AF group; 2) Trigonal copper(I) complexes with the general formula [Cu(Im)(2,2'-dipyridylamine)]BF4 in which the NHC ligands are symmetrical or not. Here again the AF substituents ensure complex stability with respect to air when compared to analogues displaying sterically non-bulky substituents. One of the complexes, namely [Cu((EtF,Ph)-Im)(2,2'-dipyridylamine)]BF4, was found to be strongly luminescent in solution and in the solid state; 3) Pd-PEPPSI complexes in which calix[4]arene-substituted phenyl moieties have been grafted on both N atoms, these behaving as potential receptor units. Owing to the presence of the calixarene termini, complexes of this type were found to self-assemble, thereby resulting in dimers with sterically highly protected metal centres. The formation of such species was correlated to the catalytic performance of these complexes.