Dissertations / Theses on the topic 'Metal carbene complex'

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.

With the blend of addressing issues of sustainable energy with the environmental worries regarding emission of greenhouse gases, there is a motivation to target the efficient chemical reduction of CO2. Re(I) integrated photosensitizers and catalysts, synthesized from commercially available ligands, are introduced with the selective CO2 reduction of formic acid, making for a unique class of Re(I) catalysts typically selective for CO as a reduction product. Furthermore, synthesized Zn(II) phosphino aminopyridine complexes are structurally and computationally characterized as well as observed to function as unprecedented electrocatalysts for the reduction of CO2 to formic acid and CO. Lastly, with the importance and popularity of N-heterocyclic carbenes (NHCs) as a class of ligands in the field of organometallic catalysis, six-membered perimidine based carbenes are further explored. Synthesis of a chelating pyridyl-perimidine NHC in addition to potential transition metal catalysts are also attempted.

Synthèse et carbonylation des complexes μ-alkylidene, en particulier fe-μ-méthylène. Mise en évidence de la réaction de dicarboxylation correspondant à l'insertion d'une molécule de Co dans chaque liaison du C en pont. Le premier intermédiaire est un complexe acyl.

ABSTRACT SYNTHESIS OF FERROCENYL CYCLOPENTENONES TUMAY, Tü
lay Asli M.S., Department of Chemistry Supervisor: Assoc. Prof. Dr. Metin Zora August 2005, 80 pages Construction of highly functionalized five-membered rings via cycloaddition reaction of cyclopropylcarbene-chromium complex with alkynes has become a very active area of research in recent years by virtue of their presence in antitumour natural products. Also with the finding that ferrocene derivatives are active against various tumours, considerable interest has been devoted to the synthesis of new ferrocene derivatives since properly functionalized ferrocene derivatives could be potential antitumour substances. So, the incorporation of the essential structural features of cyclopentenones with a ferrocene moiety could provide compounds with enhanced antitumour activities. For this purpose, we have investigated the reaction between cyclopropylcarbene-chromium complex and ferrocenyl alkynes. The reaction of cyclopropylcarbene-chromium complex with ferrocenyl alkynes afforded &
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-hydroxycyclopentenones in a one-pot process, whereas the same reaction with alkynes gave cyclopentenones as major products. Interestingly, water addition was observed instead of reduction according to the previously proposed mechanism. This is a different result than those in literature. The reaction was regioselective both with terminal ferrocenyl alkynes and internal unsymmetrical ferrocenyl alkynes. The products obtained were those where the sterically larger alkyne substituent, ferrocene, was &
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to the carbonyl group.

The work described herein focuses on the synthesis and characterisation of copper(I) complexes bearing N-heterocyclic carbene (NHC) ligands, their use in catalysis as well as organometallic synthesis and related reaction mechanisms. Two classes of complexes were considered: neutral NHC-Cu(I) species and their cationic analogues. Concerning the former, initial efforts were focused on the development of a general and straightforward synthetic methodology towards complexes of the type [Cu(X)(NHC)] (X = Cl, Br, I). More than 10 NHC-Cu(I) species were synthesised in high yields under mild conditions, in air and using technical grade solvents. These complexes exhibited interesting activity in the catalytic dehydrogenation of formic acid/amine adducts proving in three times more efficiency than the copper salts previously employed in such a reaction. Hydroxide- and tert-butoxide analogues showed to be efficient catalysts in the N-methylation of amines with CO₂ as carbon source, and in the dehydrogenative coupling of silanes and carboxylic acids. Experimental and computational work were carried out in order to elucidate the mechanism of these transformations. Regarding the use of these species in organometallic synthesis, homo- and heteroleptic bis-NHC-Cu(I) complexes were employed as carbene transfer reagents to other transition metals. Aside from well-known cationic gold(I) species, two novel palladium(II) analogues were isolated and fully characterised.

Preparation de complexes avec des coordinats cyano-4 butadienyldene portants. On obtient egalement des complexes dinucleaires avec le tricyano-3,4,4 butadienylidene-1,3. Mecanisme ses reactions de migration de l'hydrogene allylique

SYNTHESIS OF FERROCENYL CYCLOHEPTADIENONES Aç
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z, Canet M.S., Department of Chemistry Supervisor: Assoc. Prof. Dr. Metin Zora August 2005, 85 pages Synthesis of seven-membered ring systems such as cycloheptadienones has attracted a great deal of attention in organic chemistry since they are present in a variety of biologically important molecules. Incorporation of the essential structures of such compounds with a ferrocene moiety instead of an aryl group could provide subtances with enhanced antitumor activities since some ferrocene derivatives have already proved to be active against a number of tumors. To develop a ferrocenyl-substituted seven-membered ring forming reaction, we have investigated the reaction of cyclopropylcarbene-molybdenum complex with ferrocenyl-substituted alkynes. As ferrocenyl-substituted alkyne, ferrocenyl¬
propyne (25B), (2-ferrocenylethynyl)trimethylsilane (25C), 1-ferrocenyl-3-phenylprop-1-yne (25D), 1-ferrocenyl-2-phenylethyne (25E), diferrocenylethyne (25F), ferrocenyl(formyl)acetylene (25G) were synthesized starting from ethynylferrocene (25A). The reaction between cyclopropylcarbene-molybdenum complex and ferrocenyl alkynes produced ferrocenyl-substituted cycloheptadienones 26, hydrolysis product of cycloheptadienones, 27, &
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-hydroxycycloheptadienones 28 and cyclobutenones 29, depending on the substitution pattern of the alkyne moiety. Interestingly, &
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-hydroxycycloheptadienone product 28B was isolated from these types of reactions for the first time. Terminal alkynes, trimethyl- and formyl-substituted alkynes did not produce any expected product, possibly depending on the steric and electronic effects, and/or the polymerization of the alkyne. Proposed mechanism for the formation of cycloheptadienones involves metallacyclobutene formation, electrocyclic ring opening, electrocyclic ring closure, CO insertion, reductive elimination.

Ce travail de recherche est consacré au développement de catalyseurs à base de métaux de transition abondants de la première rangée du tableau périodique, tels que Mn, Fe, et Ni, pour les réactions d'hydro-élémentation. Tout d'abord, l'hydrosilylation de cétones et d'aldéhydes a été accomplie en utilisant un système catalytique simple Ni(OAc)₂ 4H2O/PCy₃ avec le PMHS, silane peu coûteux et stable en tant que source d'hydrure. L'amination réductrice d'aldéhydes avec des amines a également été réalisée avec le même système catalytique et le TMDS, comme silane. Deuxièmement, l’efficacité des complexes de manganèse demi-sandwich CpMn(CO)₂(IMes) a été prouvée pour la réduction des aldéhydes et des cétones en présence de Ph₂SiH₂ (1,5 équiv.) sous irradiation UV. La transformation difficile d'acides carboxyliques en aldéhydes a été effectuée à l'aide de Mn₂(CO)₁₀ et de Et3SiH. Troisièmement, la méthylation des amines secondaires avec le carbonate de diméthyle en tant que source C1 a été démontrée dans des conditions catalytique douces avec [CpFe(CO)₂(IMes)]I. Ensuite, l'hydroboration d'alcènes et d'alcynes fonctionnalisés a été réalisée en présence d’un complexe de fer (0), Fe(CO)₄(IMes) sous irradiation UV. Enfin, la réaction d'hydroboration a été étendue avec succès à la réduction de CO₂ en methoxyboranes avec Fe(CO)₃[P(OPh)₃]₂ en tant que catalyseur et les diverses sources de borane, tels que HBpin, HBcat ou 9-BBN
This research work deals with the use of the catalysts based on the earth-abundant transition metals of the first row of the periodic table, such as Mn, Fe, and Ni, for hydroelementation reactions. First of all, the hydrosilylation of aldehydes and ketones was accomplished using a simple Ni(OAc)₂ 4H₂O/PCy₃ catalytic system with the inexpensive and stable silane PMHS as the hydride source. The reductive amination of aldehydes with amines was also achieved with the same catalytic system and TMDS, as the silane. Second, the efficiency of manganese half-sandwich complex CpMn(CO)₂(IMes) was exemplified for the reduction of aldehydes and ketones in the presence of Ph ₂ SiH ₂ (1.5 equiv.) under UV irradiation at room temperature. Still with manganese, the challenging transformation of carboxylic acids to aldehydes was performed using commercial Mn₂ (CO)₁₀ and Et₃SiH. Third, the methylation of the secondary amines with dimethyl carbonate as an alternative and safe C1 source was demonstrated under mild conditions with [CpFe(CO)₂(IMes)]I as the catalyst. Then, the hydroboration of functionalized alkenes and alkynes was catalyzed by an iron(0) carbonyl complex Fe(CO)₄(IMes) under UV irradiation. Finally, the hydroboration reaction was successfully extended to the reduction of CO₂ to methoxyboranes with Fe(CO)₃[P(OPh)₃]₂ as the catalyst and the borane sources, such as HBpin, HBcat or 9-BBN

This thesis is comprised of two parts. The first part describes the synthesis of cyclopentadienyltungsten complexes containing a pendant alkyne group (I), and the subsequent photo-induced intramolecular coordination of the alkyne, forming complexes such as II. Compounds containing intramolecularly coordinated alkynes are rare, and this is the first example using cyclopentadiene as the core ligand. The second part describes the synthesis and structural characterisation of a number of novel metal complexes containing N-heterocyclic carbene ligands, some containing particular functionality for taylored applications. New methods were used to form complexes of rhodium, iridium, silver and gold (eg. III, IV). Structural and spectroscopic properties of the complexes were correlated with electronic characteristics of the ancillary ligands. A number of rhodium and iridium complexes (eg. IV) derived from imidazolium-linked cyclophanes were synthesised and structurally characterised. Complexes of N-heterocyclic carbenes with pendant ionic groups were synthesised, and a preliminary examination of their catalytic activity in water was performed. N-Heterocyclic carbenes complexes containing an electron withdrawing nitro group were synthesised and the effect of the nitro group on metal-ligand bonding was examined.

Des complexes de Cyclodextrine (CD)-NHC-Métaux (NHC= Carbènes N-Hétérocycliques), comprenant des métaux tel que AgI, CuI et AuI ont été synthétisés. Une étude structurale a mis en évidence la position intra-cavitaire du métal, induisant des interactions C-H…M, C-H…X et π…X. L’influence du type de cavité (α-, β-, γ-CD) et du type de dérivés NHC (Imidazole, benzimidazole, triazole) a été étudiée. Les interactions diminuent avec l’augmentation de la taille de la cavité et en parallèle, celles-ci ont été amplifiées avec des dérivés NHC possédant un effet donneur plus fort. Les complexes de cuivre correspondants montrent une bonne réactivité pour la réaction d’hydroboration des alcynes. Il a de plus été observé que la sélectivité est dépendante de la taille de la cavité. En effet, alors que le complexe α-CD-Cu donne le produit linéaire, le complexe β-CD-Cu oriente vers la formation de l’isomère branché. Les espèces CD-Cu potentiellement impliquées dans le cycle catalytique ont été étudiées. Deux mécanismes différents sont ainsi proposés. Dans la réaction catalysée par le complexe α-CD-Cu, le processus catalytique a lieu en dehors de la cavité; tandis que lorsque la cavité est plus grande (β-CD) la catalyse a lieu à l’intérieur de la celle-ci. Par ailleurs, les complexes ont également montré une différente énantiosélectivité et régiosélectivité dans une réaction de cycloisomerization catalysée par des comlexes dor, en fonction de la taille de la cavité de ces catalyseurs. Les résultats catalytiques ont prouvé que les complexes CD-NHC-Métaux fonctionnent comme des catalyseurs pour lesquels la taille de la cavité influe sur la séléctivité
Cyclodextrin (CD)-NHC-Metal complexes (NHC=N-Heterocyclic Carbene), including the AgI, CuI and AuI complexes were synthesized. A structural study showed that the metal was inside the cavity, and induced by C-H…M, C-H…X and π…X interactions. Variations on α-, β-, γ-CD cavities and NHC derivatives (midazole, benzimidazole, triazole) were studied. When the size of the cavity increased, these interactions decreased. Furthermore, stronger σ-donating effects lead to stronger interactions. CD-Cu complexes showed good activity in catalytic hydroboration of alkynes. The selectivity is depending on the size of the cavity of the catalyst. α-CD copper complex gives linear hydroboration products, while β-CD copper complex yields the branched isomers. The CD-Cu species potentially involved in the catalytic cycle were studied, two different mechanisms were thus proposed. In the α-CD-Cu complex catalyzed reactions, the catalytic process takes place outside the cavity; while a bigger cavity β-CD permits the catalysis to take place inside the cavity. Furthermore, the gold complexes also show different enantioselectivity and regioselectivity in cycloisomerization using different cavity-based catalysts. Catalytic results evidenced the selectivity of a catalytic reaction is dependent on the cavity of the CD-NHC-metal complexes

The first chapter is an introduction to the f-elements, with a focus on the synthesis and chemistry of tetravalent cerium complexes. The synthesis, characterisation and reactivity of carbenes, particularly N-heterocyclic carbenes (NHCs), and anionic-functionalised NHC ligands is discussed. The synthesis and reactivity of s-block, Group three and fblock NHC complexes is reviewed. The synthesis of the alcohol-functionalised unsaturated imidazolium proligand, [H2L]I [H2L = HOCMe2CH2(1-CH{NCHCHNiPr})], is extended to saturated imidazolinium analogues, [H2LR]X, [HOCMe2CH2(1-CH{NCH2CH2NR})]X (R = iPr, abbreviated to P; R = Mes, abbreviated to M; R = Dipp, abbreviated to D, X = Cl, I). Mono-deprotonation results in the isolation of bicyclic imidazolidines HLR, which can be ring-opened and silylated by treatment with Me3SiI, to afford [HLR, OSiMe3]I, R = iPr and Mes. Further deprotonation of HLR with MN"2 (M = Mg, Zn; N" = N(SiMe3)2) affords LRMN" (M = Mg and Zn) and ZnLR 2. These complexes proved active for the polymerisation of raclactide at room temperature without the need for an initiator. The third chapter focuses on cerium chemistry. Repetition of the literature synthesis of CeIV tert-butoxide compounds affords the unsolvated Ce(OtBu)4 and also the cluster Ce3(OtBu)11. Treatment of Ce(OtBu)4 with HL did not yield a CeIV-NHC complex, but one bearing a tethered imidazolium group, (OtBu)3Ce( -OtBu)2( -HL)Ce(OtBu)3. The synthesis of a CeIII-NHC complex, CeL3, and the oxidation of this forms an unprecedented CeIV-NHC complex, CeL4, via ligand redistribution; the complex contains two bidentate ligands and two alkoxide-tethered free NHC groups. Functionalisation of the free NHCs with boranes affords the adducts Ce(L)2(L-B)2, where B = BH3 or 9-BBN (9-Borabicyclo[3.3.1]nonane). A number of cerium complexes of the saturated-backbone NHC, LR, LRCeN"2 and LR 2CeN", have been synthesised and their oxidation chemistry and reactivity investigated. The final chapter contains an NMR study of the synthesis of a series of yttrium LR adducts, LP xYN"(3-x) (x = 1, 2 or 3), and of the synthesis of uranium complexes LRUN"2, R = Mes or Dipp, including a range of small molecule reaction chemistry. The uranyl NHC complexes, UO2LR 2, R = Mes or Dipp, have also been synthesised and characterised; these possess very high frequency carbene carbon chemical shifts.

This thesis describes the synthesis of a number of functionalised imidazolium salts as precursors to N- heterocyclic carbenes and their subsequent coordination to Ag and Pd. Further a number of the Pd complexes were tested in the Heck reaction and their activities compared to complexes with similar structural features currently within the literature. A range of imidazolium salts have been synthesised which include quinoline and octahydroacridine moieties and have been characterised by a number of methods including X-ray crystallography. A bis imidazolium salt has also been prepared as a DIOP analogue. The imidazolium salts were successfully reacted with Ag20 to form the NHCAg(I) complexes. The quinoline and octahydroacridine based NHCs were transmetallated to Pd as chelating ligands, the quinoline based systems appearing as planar, strained complexes in the X-ray structure. The activities of the quinoline and octahydroacridine based NHCPd(II) complexes in the Heck coupling of 4-bromoacetophenone and 4-chlorobenzaldehyde with n-butyl acrylate were assessed and found to be comparable to similar systems with low to satisfactory conversions.

Synthese et etude physicochimique des complexes. Reactivite. Etude cristallographique de la structure indiquant une geometrie de bipyramide trigonale deformee quand x**(-)=cl**(-),br**(-),i**(-),ncs**(-) et une geometrie de pyramide a base carree pour x=no::(2)**(-). Etude des substitutions par co,no et o::(2)

This thesis describes the synthesis of new N-heterocyclic carbene complexes through the synthesis of 1,4-bis-substituted imidazolium salts or tricyclic saturated imidazolium salts. The introduction highlights some of the most successful methods for preparing N-heterocyclic carbenes and corresponding metal complexes. Examples of the use of these complexes in transition metal-catalysed processes are provided towards the end of this chapter. The second chapter is dedicated to our efforts to synthesize 1,4-bis-substituted imidazolium salts as precursors for the synthesis of N-heterocyclic carbene complexes. The first part of this chapter describes the synthesis of 1,4-bis-substituted imidazolium salts using 1,4-bis-substituted diazabutadienes. Following this, attempts to deprotonate imidazolium salts to afford the desired N-heterocyclic carbenes are discussed. On the basis of the results obtained for the synthesis of 1,4-bis-substituted imidazol-2-ylidenes, the synthesis of N-heterocyclic carbene complexes, where the carbene is generated in situ are explored at the end of this chapter. The synthesis of enantiomerically pure tricyclic saturated imidazolium salts via enantiomerically pure diamines is discussed in the third chapter. Firstly, different methods were tested for the preparation of diamines from 6,6'-dimethyl-2,2'-bipyridine, 2,2'-biquinoline and (S,S)-6,6-bis-(1-methoxy-2,2'-dimethylpropyl)-2,2'-bipyridine. Following this, is reported the synthesis of tricyclic saturated imidazolium salts. Suzuki cross coupling of 4-chlorotoluene with phenylboronic acid was investigated in the presence of different imidazolium salts. This chapter concludes with a few suggestions for the synthesis of enantiomerically pure 2,6-bipiperidines. The fourth chapter is the experimental section and is dedicated to the methods of synthesis and characterization of the compounds mentioned in the previous chapters. X-ray reports regarding the crystallographic representation of the structures presented in chapter two and three are provided in chapter five.

Transition metal-based catalysts are one of the most powerful tools available to chemists and the development of ligand systems with which to modify their activity is a constant area of research. In the last twenty years N-Heterocyclic carbenes (NHCs) have established themselves at the forefront of organometallic chemistry. To increase the lifetime of the catalyst these ligands are increasingly being immobilised on supports as, this allows recovery and reuse while attempting to retain the activity. Cleaner, greener and safer processes are increasingly important and the recovery of the catalyst by simple separation also removes contamination and enables the possibility of re-use. This thesis describes the development of a new concept to immobilise transition metal complexes through an N-heterocyclic carbene ligand. The introductory Chapter provides an overview of transition metal catalysis, introducing the use of supported catalysis including the use of magnetic nanoparticles to aid the recovery of the catalyst systems. A discussion is included of N-heterocyclic carbene ligands, including their synthesis, activity in catalysis as ligands for metal complexes as well as attempts to support the systems and their use in various reactions. Chapter 2 provides an in-depth introduction to palladium catalysis, focusing on cross-coupling and dehalogenation reactions. The design of palladium catalysts, concentrating on palladium-NHC complexes and covers the use of supported catalysts. The synthesis and immobilisation of a novel palladium carbene complex is also described. The supported and unsupported complexes were screened in the Suzuki-Miyaura reaction and dehalogenation reaction. The activity and recycling properties of the supported catalyst system are discussed. The next Chapter outlines the use of copper-NHC complexes in the 1,3-dipolar cycloaddition reaction of azides and alkynes to form 1,2,3-triazoles. The preparation and characterisation of a novel N-heterocyclic carbene ligand is described, along with the construction of the supported copper systems. These catalysts were then investigated in the cycloaddition reaction and assessed for their activity and recovery. The scope of the reaction is also explored, investigating functional group tolerance. The final Chapter contains experimental procedures and characterisation data for all compounds synthesised during this project.

La present tesi doctoral està adreçada al desenvolupament de catalitzadors que permetin dur a terme processos sintètics de manera més eficient i sostenible. Es presenten dues noves famílies de catalitzadors suportats, ambdues pertanyents al grup de complexos organometàl·lics moleculars immobilitzats sobre un suport sòlid. La primera família inclou complexos de Pd amb lligands carbè N-heterocíclic monodentats de gran impediment estèric, immobilitzats sobre òxids inorgànics, com ara sílicas, alúmina o òxid de titani. Aquesta família de catalitzadors es va aplicar en dos tipus de reaccions: i) reaccions d'acoblament C-C i ii) semireducción d'alquins. Entre les reaccions d'acoblament esmentades, els complexos de [Pd (NHC)] immobilitzats es van aplicar a les reaccions de Suzuki, Heck i Sonogashira, i es van avaluar en base a la seva activitat, selectivitat i reciclabilitat. A més, en el cas de les reaccions de Suzuki i Sonogashira, aquests catalitzadors també es van aplicar en condicions de flux continu. L'aplicació d'aquesta família de catalitzadors en la semireducció selectiva d'alquins es va dur a terme utilitzant dues metodologies diferents: utilitzant hidrogen molecular, o bé utilitzant el sistema trietilamina / àcid fòrmic com donador de H (condicions de transferència d'hidrogen). La segona família de catalitzadors suportats contempla complexos de Rh (I) estabilitzats amb lligands bidentats de tipus carbé N-heterocíclic, amb quiralitat axial, i funcionalitzats amb un grup piré. La immobilització d'aquests complexos de Rh sobre la superfície de nanotubs de carboni "multi-walled" va tenir lloc mitjançant interaccions de tipus "pi-pi stacking" entre la superfície dels nanotubs i el grup piré present en el lligand. Finalment, es presenten els resultats obtinguts en l'aplicació d'aquests complexos de Rh en diversos processos catalítics.
La presente tesis doctoral se centra en el desarrollo de catalizadores que permitan llevar a cabo procesos sintéticos de manera más eficiente y sostenible. Se presentan dos nuevas familias de catalizadores soportados, ambas pertenecientes al grupo de complejos organometálicos moleculares inmovilizados sobre un soporte sólido. La primera familia incluye complejos de Pd con ligandos carbeno N-heterocíclico monodentados de gran impedimento estérico, inmovilizados sobre óxidos inorgánicos, como sílicas, alúmina u òxido de titanio. Esta familia de catalizadores se aplicó en dos tipos de reacciones: i) reacciones de acoplamiento C-C y ii) semireducción de alquinos. Entre las reacciones de acoplamiento mencionadas, los complejos de [Pd(NHC)] inmovilizados se aplicaron en las reacciones de Suzuki, Heck y Sonogashira, y se evaluaron en base a su actividad, selectividad y reciclabilidad. Además, en el caso de las reacciones de Suzuki y Sonogashira, estos catalizadores también se aplicaron en condiciones de flujo continuo. La aplicación de esta familia de catalizadores en la semireducción selectiva de alquinos se llevó a cabo utilizando dos metodologías diferentes: utilizando hidrógeno molecular, o bien utilizando el sistema trietilamina/ácido fórmico como dador de H (condiciones de transferencia de hidrógeno). La segunda familia de catalizadores soportados contempla complejos de Rh(I) estabilizados con ligandos bidentados de tipo carbeno N-heterocíclico, con quiralidad axial, y funcionalizados con un grupo pireno. La inmovilización de estos complejos de Rh sobre la superficie de nanotubos de carbono "multi-walled" tuvo lugar mediante interacciones de tipo "pi-pi stacking" entre la superficie de los nanotubos y el grupo pireno presente en el ligando. Finalmente, se presentan los resultados obtenidos en la aplicación de estos complejos de Rh en varios procesos catalíticos.
The present PhD thesis aims at contributing to the development of more efficient and sustainable synthetic processes through catalysis. In this regard, two families of new solid-supported catalysts are presented. Both families belong to the group of molecularly defined organometallic complexes immobilized onto a solid support. The first family includes Pd complexes of sterically hindered monodentate N-Heterocylic Carbene ligands supported onto inorganic oxide materials, namely silicas, alumina and titania. This family of catalysts was applied in two types of reactions: i) C-C cross-couplings and ii) semireduction of alkynes. Among cross-coupling reactions, the supported [Pd(NHC)] complexes could be applied in Suzuki, Heck and Sonogashira couplings and their performance was assessed in terms of activity, selectivity and reusability. For the Suzuki and Sonogashira couplings, the catalysts were also appied under continuous flow conditions. The application of this family of catalysts in the selective reduction of alkynes was carried out following two different methodologies: using hydrogen gas, or using triethylamine/formic acid as the H-donor system (transfer hydrogenation conditions). The second family of solid-supported catalysts features Rh(I) complexes bearing axially chiral bidentate N-Heterocyclic carbene ligands functionalized with a pyrene moiety. Immobilization of these Rh complexes onto the surface of multi-walled carbon nanotubes was achieved by means of "pi-pi stacking interactions" between the surface of the nanotubes and the pyrene moiety present in the ligand. Results obtained from the application of these complexes as catalysts in various reactions are presented.

This thesis describes the synthesis of a series of Ag(I), Pd(II), Rh(I) and Ir(I) complexes of quinoline functionalised nucleophilic heterocyclic carbene (NHC) ligands. The transmetallation properties of the Ag(I) complexes were utilised to prepare the corresponding Pd(II), Rh (I) and Ir(I) (NHC) complexes. A series of quinoline based imidazolium, pyrimidinium salts were prepared and characterised as NHC ligand precursors. Ag(I)(NHC) complexes were prepared by the reaction of the quinoline functionalised salts with Ag20 in DCM. All complexes were spectroscopically characterised and the results of single X- ray crystallographic studies are reported for two of the complexes and the geometry around the silver cation was observed to be distorted linear. Two quinoline based palladium (II) (NHC) complexes were prepared via transmetallation Ag(I)(NHC) complexes is reported. The synthesis of a series of methylene bridged quinoline functionalised Rh (I) and Ir(I) (NHC) complexes through transmetallation of the Ag(I)(NHC) complexes is reported and the results of single X-ray crystallographic studies are reported for most of the complexes showing consistent pattern in term of bond lengths and angles. Two of the Ir(I) (NHC) complexes were tested as catalysts in transfer hydrogenation reactions, showing good activity at low Ir loadings.

N-Heterocyclic Carbenes (NHC) present a viable alternative to traditional phosphine ligands in a variety of organometallic mediated catalytic reactions. Singlet ground-state carbenes are stabilized by the push-pull presence of two adjacent nitrogen atoms in an imidizolium 5-membered ring, allowing neutral electron donor properties. The ability to synthesize a variety of NHC ligands with differing steric and electronic properties is possible by changing the sustiuents on the nitrogen atoms of the imidizolium. Tunable characteristics and enhanced chemical and thermal stability give NHC’s an advantage over phosphines in many catalytic systems. This dissertation focuses on the use N-Hetercyclic Carbenes in a variety of organometallic complexes. The synthesis of NHC complexes with a variety of transition metals is described. The transition metals complexed with NHC’s include palladium, iridium, nickel and ruthenium. The catalytic activity of the metal-NHC complexes is investigated as well.

Fischer carbene complexes of the Group VI transition metals (Cr, Mo and W) containing at least two or three different transition metal substituents, all in electronic contact with the carbene carbon atom, were synthesized and studied both in solution and in the solid state. For the complexes of the type [M(CO)5{C(OR)R’}], the substituents chosen included (hetero)aromatic (benzene or thiophene) rings π-bonded to a chromium tricarbonyl fragment or ferrocene as the R’-substituent, while the OR-substituent was systematically varied between an ethoxy or a titanoxy group, to yield the complexes 1 (M = Cr, R = Et, R’ = Fc), 2 (M = W, R = Et, R’ = Fc), 5 (M = Cr, R = TiCp2Cl, R’ = Fc), 6 (M = W, R = TiCp2Cl, R’ = Fc), 7 (M = Mo, R = TiCp2Cl, R’ = Fc), 12 (M = Cr, R = TiCp2Cl, R’ = 2-thienyl) and 13 (M = Cr, R = TiCp2Cl, R’ = [Cr(CO) 3 (η 6-phenyl)]). Direct lithiation of the ferrocene with n-BuLi/TMEDA at elevated temperatures, followed by the Fischer method of carbene preparation, also resulted, in most cases, in the formation of the novel biscarbene complexes with bridging ferrocen- 1,1’-diyl carbene ligands [μ-Fe{C5H4C(OEt)M(CO) sub>5}2] (3: M = Cr, 4: M = W) or the unusual bimetallacyclic bridged biscarbene complexes [{μ-TiCp2O2-O,O’}{μ- Fe(C5H4)2-C,C’}{CM(CO) 5}2] (8: M = Cr, 9: M = W, 10: M = Mo). It was attempted to prepare the mixed heteronuclear biscarbene complex 11 [W(CO) 5C{μ-TiCp2O2- O,O’}{μ-Fe(C5H4)2-C,C’}CCr(CO) 5], however the complex could not be fully characterized. The investigation was expanded to include Group VII transition metals Mn and Re, and using the same methodology, the manganese complexes isolated included [MnCp(CO2{C(OR)Fc}] (22: R = Et, 24: R = TiCp2Cl), 23 [μ- Fe{C5H4C(OEt)MnCp(CO) 2}2] and 25 [{μ-TiCp2O2-O,O’}{μ- Fe(C5H4)2- C,C’}[CMnCp(CO) 2}2]. The different reactivity of the binary dirhenium decacarbonyl precursor complex, compared to that of the Group VI complexes, resulted in the formation of a range of complexes. The target compounds [Re2 (CO) 9{C(OR)Fc}] (26: R = Et, 31: R = TiCp2Cl), 27 [μ-Fe{C5H4C(OEt)Re2 (CO) 9}2] and 33 [{μ- TiCp2O2-O,O’}{μ-Fe(C5H4)2-C,C’}[CRe2 (CO) 9}2] were isolated displaying a variety of different geometric isomers. In addition, acyl (30) and aldehyde (32) decomposition products, as well as hydrido (29), and hydrido acyl hydroxycarbene (34) complexes and the unique dichloro-bridged biscarbene complex (28) were also characterized. Most of these complexes displayed Re-Re bond breaking, and two probable mechanisms, either radical or ionic, were proposed involving either hydrogen transfer or protonation followed by hydrolysis. Finally, the structural features and their relevance to bonding in the carbene cluster compounds of the Group VI transition metals were investigated as they represent indicators of possible reactivity sites in multimetal carbene assemblies. The possibility of using DFT calculations to quantify the effect of metal-containing substituents on the carbene ligands was tested and correlated with experimental parameters by employing methods such as vibrational spectroscopy, molecular orbital analysis, and cyclic voltammetry. The best results were obtained from the cyclic voltammetric studies, where the localized metal centre’s oxidation potential correlated to both the calculated HOMO energy, and the effect of both the heteroatom substituent and the (hetero)arene substituent, as well as different combinations of the above.
Thesis (PhD)--University of Pretoria, 2010.
Chemistry
unrestricted

The combination of Lewis acidic f-block metals and a labile nucleophilic carbene can be an excellent means to activate small molecules such as silanes, CO2 and other traditionally inert substrates. Furthermore, bidentate alkoxy-NHC ligands have shown promise in the support of unusual high oxidation state organometallic complexes, including examples of CeIV, PdIV and UVI. In this thesis the synthesis and reactivity of a series of f-block metal NHC complexes is described. Chapter One introduces N-heterocyclic carbenes and their f-block metal complexes, in particular of cerium, praseodymium and uranium. Furthermore, it will give an overview of small molecule activation by NHCs, lanthanides and specifically [Ce(LAr)N"], (L = OC(CH3)2CH2(CNCH2CH2NMes) the magnetic properties and use of lanthanides e.g. as single molecule magnets and oxo-functionalisation of the uranyl moiety. Chapter Two describes the addition-elimination reaction chemistry of CeIII and UIV NHC complexes in which polar reagents add in a heterocyclic fashion across the MNHC bond. It also describes the synthesis of the lithium salt of the alkoxycarbene proligand [LiLAr]4 and its reactivity towards f-element halide and aryloxide salts. A series of reactions to target the formation of metal-metal bonds is described. Chapter Three focuses on the synthesis of novel cerium and praseodymium complexes [Pr(LAr)N"2], [Pr(LAr)2N"], [Pr(OAr2,6-tBu)3] and [Ce(OAr2,6-tBu)3] and their reactivity towards oxidants. A series of alkoxide bridged lanthanide dimers [(Cl)Ce(μ- LAr)2Ce(Cl)2], [N"(LAr)Ce(μ-OAr2,6-tBu)OAr2,6- 2Ce(LAr)N"] and [N"(Cl)Pr(μ LAr)2Pr(Cl)N"] have been made and characterised including by SQUID variable temperature magnetometry. Chapter Four evaluates the synthesis and reactivity of uranyl complexes [UO2(LAr)2], [UO2N"2(py)2] and [UO2(OAr2,6-tBu)2(py)2], specifically their reactivity towards haloboranes in different solvents. Additionally, the oxo-functionalisation of uranyl compounds with haloboranes is discussed. Chapter Five draws conclusions and provides a summary of the work presented. Chapter Six comprises the experimental details and analytical data.

L’objectif de ce travail est la synthèse de complexes contenant des ligands NHC protiques fonctionnalisés avec un groupement imine dans le but de développer des méthodologies de synthèse donnant accès à des ligands pNHC ainsi que la synthèse des groupes imidazolide anioniques liés par le C et leurs complexes homo et hétéro-dinucléaires. Dans le cas des imidazoles sans groupe fonctionnel, la déprotonation à l’aide de n-butyl lithium a permis l’obtention de (1-aryl-1H-imidazol-2-yl)lithium avec de bons rendements. La réaction de (1-aryl-1H-imidazol-2-yl)lithium avec [Ir(cod)(μ-Cl)]2 ou [Rh(cod)(μ-Cl)]2 a conduit à des complexes dinucléaires bipontés en C2,N3. Dans le cas de l’imidazole possédant une fonctionnalité imine, le complexe de l’Ir(I) lié au N de l’imidazole peut se tautomériser en complexe de l’Ir(I) imine avec un ligand pNHC suite à la réaction d’abstraction du chlorure à température ambiante, alors que la tautomérisation de l’analogue du Rh(I) nécessite une température de 110°C. La déprotonation des complexes de l’Ir(I) et Rh(I) liés par le N de l’imidazole avec addition de [Ir(cod)(μ-Cl)]2 ou de [Rh(cod)(μ-Cl)]2 in situ permet l’obtention de complexes homo et hétéro-dinucléaires. La métallation des sels d’imidazolium fonctionnalisés avec un groupement imine s’est avére être une méthode efficace pour la synthèse de complexes métallés ayant un ligand pNHC et a été étendue des complexes bidentes aux complexes chélatants pNHC
The purpose of this work is the synthesis of complexes containing imine-functionalized protic NHC ligands in order to further develop synthetic methodologies giving access to pNHC, C-bound ‘anionic’ imidazolide, and homo- and heterodinuclear complexes. In the case of imidazoles without functional group, deprotonation with n-butyl lithium afforded (1-aryl-1H-imidazol-2-yl)lithium in good yield. Reaction of (1-aryl-1H-imidazol-2-yl)lithium with [Ir(cod)(μ-Cl)]2 or [Rh(cod)(μ-Cl)]2 yielded a doubly C2,N3-bridged dinuclear complex. In the case of imine-functionalized imidazole, the Ir(I) N-bound imidazole complex can tautomerize to Ir(I) imine-functionalized pNHC complex chloride abstraction at room temperature, while in the Rh(I) analog the tautomerization can be achieved at 110 °C. In situ deprotonation of the N-bound imidazole Ir(I) or Rh(I) complexes, followed by addition of [Ir(cod)(μ-Cl)]2 or [Rh(cod)(μ-Cl)]2 led to the isolation of homo- and heterodinuclear complexes. The metalation of imine-functionalized imidazolium salts is also an effective procedure for synthesis of pNHC metal complexes, and it was extended from bidentate to pincer-type pNHC complexes

The versatility of N-heterocyclic carbenes (NHCs) is demonstrated by numerous practical applications in homogeneous transition metal catalysis, organocatalysis and materials science. There remains a paucity of electropositive metal NHC complexes and so this chemistry is poorly developed with respect to that of the late transition metal and main group elements. This thesis describes the synthesis of new alkoxy-tethered NHC proligands, their use in the synthesis of reactive metal amide and metal alkyl complexes, and finally small molecule activation using these complexes. Chapter One introduces NHCs and discusses their use as supporting ligands for early transition metal and f-block complexes. Small molecule activation using organometallic complexes is examined alongside the use of electropositive metal NHC complexes in catalysis. Chapter Two contains the synthesis and characterisation of new alkoxy-tethered NHC proligands and a variety of electropositive MII (M = Mg and Zn), MIII (M = Y, Sc, Ce and U) and MIV (M = Ce and U) amide complexes. X-ray diffraction studies and a DFT study are used to probe the extent of covalency in the bonding of the MIV complexes. Chapter Three investigates the reactivity of the amide complexes prepared in Chapter Two. The MII complexes are shown to be initiators for the polymerisation of raclactide into biodegradable polymers. The MIII complexes are used to demonstrate additionelimination reactivity of polar substrates across the M-Ccarbene bond which allows the formation of new N-E (E = Si, Sn, P or B) bonds. Treatment of the UIII silylamide complex U(N{SiMe3}2)3 with CO results in the reductive coupling and homologation of CO to form an ynediolate core -OC≡CO- and the first example of subsequent reactivity of the ynediolate group. The MIV complexes are used to examine the potential for forming MIV cationic species and alkyl complexes. Chapter Four examines the synthesis of MIII (M = Ce and Sc) aminobenzyl complexes and MIII (M = Y, Sc and U) neosilyl and neopentyl alkyl complexes. The addition-elimination reactivity discussed in Chapter Three is extended to include C-E bond formation (E = Si, Sn, P, B, I or C). Chapter Five provides overall conclusions to the work presented within this thesis. Chapter Six gives experimental and characterising data for all complexes and reactions in this work.

Thesis (PhD (Chemistry and Polymer Science))--University of Stellenbosch,2005.
This study comprises the preparation and full characterisation of new carbene complexes of group 10 metals (Ni, Pd or Pt), the group 9 metal, rhodium, as well as group 6 metals (Cr and/or W). N-heterocyclic carbene (NHC) complexes of nickel and palladium were prepared via oxidative addition of the corresponding carbene precursors imidazolium-, imidazolinium-, pyridinium- and quinolinium chloride salts, to M(PPh3)4 (M = Ni or Pd). Three types of carbene complexes, namely the standard five-membered two-N carbene complexes, new six-membered NHC complexes and novel six-membered rNHC complexes received attention. In the rNHC complexes the heteroatom (N) is removed from the carbene carbon. These new square planar carbene complexes of the general formula trans-[(PPh3)2MCl(L)]X (M = Ni or Pd; X = BF4 or PF6) L = 1,3-dimethyl-2,3-dihydro-1Himidazol- 2-ylidene, 1,3-dimethyl-2,3,4,5-tetrahydro-1H-imidazol-2-ylidene, 1-methyl-1,2-dihydropyridin- 2-ylidene, 1-methyl-1,2-dihydro-quinolin-2-ylidene, 1,4-dimethyl-1,2-dihydro-quinolin-2- ylidene, 2-methoxy-1-methyl-1,4-dihydro-quinolin-4-ylidene, 1-methyl-1,4-dihydro-pyridin-4- ylidene) have been isolated and characterised. The preparation of the corresponding carbene complexes of platinum was complicated by the formation of [PtCl(PPh3)3]BF4 and the desired carbene complexes could not be isolated in pure form. The investigation of rNHC complexes was extended to include the synthesis of (CO)5M{CSC(CNCMe2CH2O)CHCH} (M = Cr and W). The molecular and crystal structures of thirteen of the new carbene complexes including the structures of both cis- (only formed below –20°C) and trans-chloro(1-methyl-1,2-dihydro-quinolin- 2-ylidene)bis(triphenylphosphine)palladium(II) tetrafluoroborate were determined. The metalcarbene bond distances in both the palladium and nickel carbene families do not differ significantly. The carbene ligands can be arranged in a series of increasing trans-influence, using the metalchloride bond distance as a guideline, as follows: 1,3-dimethyl-2,3-dihydro-1H-imidazol-2-ylidene and 1,3-dimethyl-2,3,4,5-tetrahydro-1H-imidazol-2-ylidene < 1-methyl-1,2-dihydro-pyridin-2- ylidene < 2-methoxy-1-methyl-1,4-dihydro-quinolin-4-ylidene, 1-methyl-1,4-dihydro-pyridin-4- ylidene. The crystal and molecular structures of two platinum compounds, cis-chloro(2-methoxy-1- methyl-1,4-dihydro-quinolin-4-ylidene)bis(triphenylphosphine)platinum(II) tetrafluoroborate and the byproduct [PtCl(PPh3)3]BF4 were also determined. Trans-chloro(2-methoxy-1-methyl-1,4-dihydro-quinolin-4-ylidene)bis(triphenylphosphine) palladium(II) tetrafluoroborate was found to be a very active catalyst, compared to simpler palladium carbene and phosphine complexes, in the Mizoroki-Heck and Suzuki-Miyaura coupling reactions. Quantum mechanical calculations indicated that the rNHC ligand in this complex is bound stronger to the palladium than a standard imidazole-derived NHC ligand. Further calculations suggested that the remote heteroatom carbene (rNHC) complexes of nickel(II) are significantly more stable when compared to the normal carbene (NHC) complexes. Energy decomposition analysis suggested that the rNHC ligands are strong s-donors and weak -acceptors. Unsymmetrical imidazolium-derived bis(carbene) complexes, [Rh(NHC)2COD]Br, bromomono( carbene) complexes, Rh(Br)COD(NHC), and chloro-mono(carbene) complexes, Rh(Cl)COD(NHC) where NHC = 1-R-3-methyl-2,3-dihydro-1H-imidazol-2-ylidene (R = ethyl, propyl or butyl), were formed in each reaction of the corresponding free carbene ligand with [Rh(Cl)COD]2. [Rh(Br)COD(NHC)] formed as a result of substitution of a chloride ligand by a Br-- anion. The carbonyl complexes, cis-[Rh(CO)2X(NHC)] (X = Br or Cl; NHC = 1-ethyl-3-methyl- 2,3-dihydro-1H-imidazol-2-ylidene) were isolated after the substitution of the COD ligand in Rh(X)COD(NHC) (X = Br or Cl) with CO. Isomerisation of these cis-carbonyl complexes to the trans isomers was observed. Cis-[(h4-1,5-cyclooctadiene)bis(1-butyl-3-methyl-2,3-dihydro-1H-imidazol-2-ylidene)rhodium(I)] bromide, bromo(h4-1,5-cyclooctadiene)(1-methyl-3-propyl-2,3-dihydro-1H-imidazol-2-ylidene) rhodium(I) and cis-[(h4-1,5-cyclooctadiene)bis(1-butyl-3-methyl-2,3-dihydro-1H-imidazol-2- ylidene)rhodium(I)]bromide were also characterised by single crystal X-ray diffraction. The synthesis and structural characterisation of a series of acyclic and heterometallacyclic Fischertype carbene complexes in which a soft donor atom (P) attached to the carbene side chain is either uncoordinated, (CO)5M=C(NMe2)CH2PPh2 (M = Cr or W), bonded to the original central metals (Cr or W) in four-membered chelates, (CO)4M=C(NMe2)CH2PPh2, or coordinated to a second M(CO)5 unit (only isolated for chromium) (CO)5Cr=C(NMe2)CH2P(Ph2)Cr(CO)5, were carried out. These compounds were produced by the reaction of the anionic Fischer-type aminocarbene complexes, [(CO)5Cr=C(NMe2)CH2]Li (M = Cr or W), with ClPPh2. The formation of the four-membered chelates, via cyclisation, occurs much faster for Cr than for W. The aminocarbene-phosphine chelates represent the first examples of structurally characterised, four-membered C,P-chelate carbene complexes.

Chapter one is an introduction, outlining the structure and bonding of N-heterocyclic carbenes (NHCs). It then goes on to give examples of f -metal NHC complexes and describes any reactivity or catalytic activity. Chapter two describes the synthesis of the transition metal NHC complexes [Fe (LMes)2] 3 and [Co(LMes)2] 4 (LMes = OCMe2 CH2(1-C{NCH2CH2NMes})). The heterobimetallic complexes [(LMes)Fe(μ-LMes)U(μ-{N(SiMe3)Si(Me)2CH2})(N(Si Me3)2)2] 5 and [(LMes)Co(μ-LMes)U(μ-{N(SiMe3)Si(Me)2CH2})(N(SiMe3)2)2] 6 were prepared from the reaction between [({Me3Si}2N)2U(NSiMe3SiMe2CH2)] and 3 or 4, respectively. Complex 5 was also synthesised by the reaction between 3 and [U(N{SiMe3}2)2]. The diamagnetic analogue [(LMes)Zn(μ-LMes)Th(μ-{N(SiMe3)Si (Me)2CH2})(N(SiMe3)2)2] 9 was prepared from the reaction between [Zn(LMes)2] and [({SiMe3}2N)2Th(NSiMe3SiMe2CH2)]. The reactivity of 5 is discussed. When 5 was reacted with 2,6-dimethylphenyl isocyanide, [({SiMe3}2N)2U{N(SiMe3)Si(Me2)C(CH2)N(2,6−Me−C6H3)}] 8 was isolated. The reaction with CO resulted in the formation of [({Me3Si}2N)2U{N(SiMe3) Si(Me2)C(CH2)CO}]. 5 showed no reactivity with azides, boranes or m-chloroperbenzoic acid and decomposed when exposed to H2, CO2 or KC8. The reaction between 6 and 2,6-di-tert-butylphenol formed the previously reported monometallic complex [({SiMe3}2N)2U(OC6H3tBu2)]. The serendipitous synthesis of the iron ate complex [Na(Fe{LMes}2)2]+ [Fe(ArO)3]– 10 (Ar = 2,6-tBu-C6H3) is also described. Chapter three describes the synthesis of the aryloxide complexes [HC(3-tBu-5-Me- C6H2OH)(3-tBu-5-Me-C6H2O)μ-(3-tBu-5-Me-C6H2O)Co(THF)]2 11 and [HC(3- tBu-5-Me-C6H2OH)(3-tBu-5-Me-C6H2O)μ-(3-tBu-5-Me-C6H2O)Zn(THF)n] 13. Treatment of 11 with pyridine N-oxide resulted in the formation of the pyridine-Noxide adduct [HC(3-tBu-5-Me-C6H2OH)(3-tBu-5-Me-C6H2O)μ-(3-tBu-5-Me-C6H2 O)Co(C5H5NO)]2 12. When 11 was treated with [({Me3Si}2N)2U(NSiMe3SiMe2C H2)], no reaction occured at room temperature but at 80◦C decomposition occured. When 11 was treated with [(NH4)2Ce(NO3)6] the protonated proligand HC(3-tBu- 5-Me-C6H2OH)3 reformed. The reactivity of 11 with [({Me3Si}2N)Ce(LiPr)2] is also discussed. Chapter three also discusses the preparation of the heterobimetallic complex [HC(3- tBu-5-Me-C6H2O)2-μ-(3-tBu-5-Me-C6H2O)KCo]2 14 and the salt-elimination chemistry of the complex. The preparation of [HC(3-tBu-5-Me-C6H2O)2-μ-(3-tBu-5- Me-C6H2O)KZn]2 15 is also outlined. Chapter four discusses the reactivity of [Ce(LiPr)3] (Li Pr =OCMe2CH2(1-C{NCHC HNiPr})) in C-H and N-H activation and as a catalyst for organic reactions. [Ce(LiPr)3] displayed no C-H activation chemistry with RC−−−CH (R = SiMe3, Ph, tBu), diphenyl acetone, indene or fluorene. [Ce(LiPr)3] also showed no N-H activation chemistry with pyrrole or indole, nor did it react with the lignin model compound PhOCH2Ph. When treated with an excess of benzyl chloride, [Ce(LiPr)3] underwent ligand decomposition to form the acylazolium chloride [(C6H5C(O))OCMe2CH2(1-C(C6H5C (O)){NCHCHNiPr})]Cl 18 and CeCl3. When [Ce(LiPr)3] was added to a mixture of benzaldehyde and benzyl chloride, as a coupling catalyst, the complex decomposed. [Ce(LiPr)4] was tested as a catalyst from the benzoin condensation and for the coupling of benzalehyde and benzyl chloride, however, it resulted in the decomposition of [Ce(LiPr)4]. Chapter four also outlines the catalytic activity of 3. The complex showed no reactivity as a hydrogenation catalyst towards alkenes, aldehydes or ketones but did display reactivity as a hydroboration catalyst for alkenes, aldehydes or ketones. Chapter five presents the conclusions for chapters two to four. The final chapter contains the experimental details from the previous chapters.

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.

Le travail de thèse, en co-tutelle entre l'Université de Padoue et l'Université de Strasbourg, se concentre sur la chimie des carbènes bis-(N-hétérocycliques) et peut être divisé en quatre familles de ligands qui constituent les quatre chapitres du manuscript : i) complexes métalliques de Cu(I), Ag(I), Au(I), Ir(III) et Ru(II) avec des ligands di(carbène N-hétérocyclique) portant un pont phénylène rigide entre les unités carbèniques; ii) complexes métalliques de Cu(I), Ag(I), Au(I) et Ru(II) combinant un ligand NHC fonctionnalisé avec un triazole dans la position 5 du squelette; iii) complexes métalliques d’Ag(I), Au(I) et Pd(II) avec des ligands hétéroditopiques à base d'un imidazol-2-ylidène et d’un 1,2,3-triazol-5-ylidène reliés par un pont propylène; iv) proligands bis (benzoxazoles) et les tentatives de complexation sur des métaux de transition
The PhD, a collaboration between the University of Padova and the University of Strasbourg, is focused on the chemistry of di(N-heterocyclic carbene) ligands and can be divided in four families of ligands that constitute the four chapters: i) metal complexes (Cu(I), Ag(I), Au(I), Ir(III), Ru(II)) with di(N-heterocyclic carbene) ligands bearing a rigid phenylene bridge between the carbene units; ii) metal complexes (Cu(I), Ag(I), Au(I), Ru(II)) combining an imidazole-based NHC ligand functionalized with a triazole in the 5 position of the backbone; iii) metal complexes (Ag(I), Au(I), Pd(II)) with heteroditopic ligands based on imidazol-2-ylidene and 1,2,3-triazol-5-ylidene moieties connected with a propylene bridge; iv) bis(benzoxazolium) proligands and attempted synthesis of related transition metal complex

This thesis presents an investigation into the synthesis of metal complexes of (Nheterocyclic carbene)-based cyclophanes. There were three main areas of focus: synthesis and complexation of bis(4,5-dihydroimidazolium) salts; the synthesis and complexation of phenol-functionalised imidazolium cyclophanes; and the synthesis and complexation of (N-heterocyclic carbene)-based cyclophanes by C-C bond activation of biimidazolium salts with electron-rich metals. The synthesis of xylyl-linked bis(4,5-dihydroimidazolium) salts was investigated. Attempts to prepare these compounds by the cyclisation of a tetraamine (linear or macrocyclic) were unsuccessful due difficulties in preparing the tetraamines. The target compounds could be prepared by adapting the methods developed for the synthesis of bis(imidazolium) salts however problems associated with purification and stability of the products prevented complexation studies. A series of phenol-, phenoxide- and anisole-functionalised imidazolium cyclophanes were prepared. Their structural properties were investigated using dynamic nmr studies and X-ray crystallography. Complexation of the functionalised cyclophanes was investigated. The phenol cyclophane I formed a dinuclear complex with mercury(II). This complex is the first example of a complex derived from a phenol-functionalised imidazolium cyclophane. However the anisole cyclophane II and the unsymmetrical phenol/ortho cyclophane III were unable to form complexes possibly due to steric hindrance and instability of the cyclophane respectively. Preliminary complexation studies of the bis(imidazolium)phenol V suggested that complexation with palladium(II) and mercury(II) were possible but more work is required to determine the optimum reaction conditions. A series of biimidazolium salts VI (both new and known) were prepared. Previously reported biimidazolium salts have very low solubility in common solvents therefore the incorporation of long alkyl chains to the bridging group was investigated as a means to improve the solubility. The structure of the salts was explored using a range of techniques including dynamic nmr spectroscopy, cyclic voltammetry, UV/Visible spectroscopy, X-ray crystallography and mass spectrometry. Some of the biimidazolium salts were able to rotate about the C2-C2' bond and the free energy of activation for this process was estimated using dynamic nmr studies. C-C bond activation of the biimidazolium salts with palladium(0) was used to form a series of palladium(II) complexes (VII) of (NHC)-based cyclophanes. These reactions are the first examples of the synthesis of bis(NHC) complexes by C-C bond activation. The reactivity of the biimidazolium salts with palladium(0) was compared to their solution structure and it was found that only the biimidazolium that were able to rotate about the C2-C2' bond could react with palladium(0).

The syntheses of a new class of polycyclic TriAmino DiCarbenes (TADCs), based on 3,9-diazajulolidine, and their precursors and adducts are described. Starting with 2,6-dimethyl-nitrobenzene, 2,6-bis ((alkylamino)methyl)anilines (alkyl = isopropyl, mesityl, and tert-butyl) were synthesized in 40% yield over five steps. These triamines were then di-cyclized stepwise to diformamidinium dications or formamidinium/2-methoxyformaminals using oxonium salts and trialkyl orthoformates. A diformamidinium dication was characterized by single-crystal X-ray diffractometry. Treatment with various bases, particularly lithium hexamethyldisilylazide, led to the novel TADCs and monocarbenes, two of which were isolated and characterized by 1H and 13C NMR spectroscopies. In both cases, treatment with elemental sulfur trapped the TADCs as dithiobiurets. No TADC-transition metal complexes were successfully isolated from reactions of the diformamidinium dications or LiHMDS TADC complex with a number of transition metal complexes. With the exception of these two cases, all other TADCs were not isolated because they rapidly reacted to form dimers, trimers, and tetramers. One of these dimers was isolated and its structure determined using 1D and 2D NMR spectroscopies, along with high-resolution electrospray ionization mass spectrometry. This revealed that the TADC had dimerized to form an ene-triamine, likely via 1,3-shift of a benzylic proton. Novel N-heterocyclic Carbene (NHC) complexes of molybdenum were also synthesized and characterized. Reaction of Cp2Mo2(CO)4 (Cp = C5H5) with dimesityl-imidazol-2-ylidenes (IMes) or dimesityl-imidazolidin-2-ylidenes (SIMes) yielded the molybdoradicals CpMo(CO)2(NHC) (NHC = IMes or SIMes). The carbonyl infrared stretching frequencies and the relative metal-to-NHC π-backbonding for IMes and SIMes complexes are compared. Reaction of the less bulky dimethyl-imidazol-2-ylidene (IMe) with Cp2Mo2(CO)4 yielded the Mo-Mo triple bond complex Cp2Mo2(CO)3(IMe) by CO substitution. This is the first example of an NHC-ligated metal-metal multiply bonded complex. Single crystal X-ray diffractometry of these new organomolybdenum and organodimolybdenum complexes is discussed.

The discovery of N-heterocyclic carbenes (NHC) has dramatically affected the world of catalysis. Their inherent properties that make them excellent auxiliary ligands for catalytic processes have countless laboratories worldwide probing and exploiting every notable feature they possess. However, while there is no shortage of attention in this field of research, there has been considerably less interest in NHCs with an ability chelate to metals via a mixed-donor ligand architecture. Thus, this thesis describes the synthesis and application of a ligand set comprised of bidentate mixed-donor NHC ligands. The ligands prepared all contain a mesitylimidazol-2-ylidene core unit, but incorporate different donor-functionalized tethers. These mixed-donor NHC ligands are synthesized by using a strong base, such as KN(SiMe₃)₂, to deprotonate the imidazolium salt precursors. This strategy was used to effectively prepare 1-mesityl-3-(2-(mesitylamino)ethyl)imidazol-2-ylidene, Mes[CNH] and 1-mesityl-3-(2-aminoethyl)imidazol-2-ylidene, Mes[CNH₂]. Mes[CNH] was found to be a convenient proligand for the synthesis of various M-NHC (M = Rh, Ir, Ru, Pd, Ni, Fe, Ag, Li) compounds. These Mes[CNH]-M complexes demonstrated the hemilabile character of the Mes[CNH] ligand forming complexes that incorporated either a coordinated or uncoordinated amino tether. Mes[CNH]M(diene)Cl, Mes[CN]M(diene) and [Mes[CNH]M(diene)]BF₄(M = Rh, Ir; diene = 1,5-cyclooctadiene, 2,5-norbornadiene) were synthesized and investigated for their ability to perform hydrogenation and hydrosilylation reactions with various substrates. Mes[CNH]Ru(=CHPh)(PCy₃)Cl₂, Mes[CNH]Ru(=CHPh)(py)Cl₂ (py = pyridine) and Mes[CNH]Ru(=CHPh)(PMe₃)Cl₂ were also synthesized and fully characterized. The activity of the former two Ru complexes was studied for their ability to catalyze ring-closing metathesis (RCM) and ring-opening metathesis polymerization (ROMP) reactions. In addition, the phosphine dissociation rate of Mes[CNH]Ru(=CHPh)(PCy₃)Cl₂ was measured via magnetization transfer experiments and compared to other known Ru-benzylidene analogues. In addition to the amino-tethered NHC proligands, a phosphine analogue Mes[CP] was prepared and its reactivity with late transition metal complexes was investigated. While the free NHC-phosphine species could not be isolated, deprotonation of both the iminium and phosphine protons followed by the addition of [M(COD)Cl]₂ (M = Rh, Ir) yields Mes[CP]M(COD), which incorporates a bidentate NHC-phosphide ligand. Mes[CP]Ir(COD) was then investigated for its ability to perform hydrogenation and benchmarked to its Mes[CN]Ir(COD) analogue.

A new (CNC) pmcer ligand, (2,6-bis(2,6-diisopropylphenyl)imidazol-2-ylidene)-3,5dimethylpyridine, has been synthesised. the previously reported ligand (2,6bis( 2,6-diisopropylphenyl)imidazol-2-ylidene)pyridine, (CNC) pincer complexes of transition metals across the from titanium to iridium, have been synthesised, fully characterised and investigated. NHCs, trialkylphosphines and imines as canied out. complexes of (CNC) and (PNP) were better a-donors than tpJI,;TP) ligands, in complexes of (CNC), (PNP) and (NNN) better a-donors, contrary to literature reports. keeping ligands A comparison of the cr-dlon:ltlnlg nroDlerties part of pincer ligands ligands revealed to coordinated vinyl groups have been observed (CNC) ligands. Proposed mechanisms indicate the to the CNHC followed by base-catalysed thougflt the latter occurs via a 4-membered nitrogenbinding mode for NnCs also been un:suullrated backbone of an imidazol-2-ylidene ring bonds in an 172 is centre.

This thesis describes the theoretical and experimental study of group 9 and 10 transition metal N-heterocyclic carbene complexes in catalytic reactions. In order to overcome decomposition reactions discovered in the use of carbene complexes for carbon monoxide/ethylene copolymerisation, chelating thiazolium salts were prepared for the synthesis of corresponding palladium complexes. Complex formation proved difficult and experimental attempts to overcome possible side reactions caused by reactant-metal interactions were unsuccessful. Theoretical studies indicated a sulfur-palladium interaction may be contributing to alternative products, with the use of the bulky lBu coordination at the thiazolium 5 position likely to block this interaction enough to allow C2 carbene formation. Theoretical calculations for the oxidative addition of azolium salts to a model Wilkinson's catalyst (RhCl(PH3)3) is described. According to free energy calculations, a six ligand associative route with a concerted three-centred transition structure may be competitive to a route in which phosphine predissociation occurs. Exchange of the phosphine molecule on the metal centre with trimethylphosphine had a significant effect in lowering the barrier to oxidative addition and decreasing the endothermicity of the reaction, while explicit and bulk solvation was found to have a moderate effect on the overall reaction. Extension of the oxidative addition of azolium salts to rhodium carbene complexes have been examined, in which a range of ligands is described from the pi-acidic carbon monoxide ligand to multiple carbene ligands. Increasing basicity decreases activation barriers while increasing the exothermicity of the overall reaction for C-H activation, however the complex most successful at C-H activation was not considered hospitable enough for related C-C activation of 2-methylazolium salts. Switching to iridium indicated a large benefit in C-H activation. Unfortunately, C-C activation remained unfavourable for iridium due to a high barrier to reaction. A mechanism for the experimentally successful C-C coupling of azolium salts to alkenes by nickel complexes is studied, indicating an oxidative addition, alkene insertion and reductive elimination cycle seems likely. Experimentally, the switching of catalytically active phosphine ligands to the related carbenes causes the reaction to be halted. Theoretical calculations imply minor changes to reaction conditions may significantly affect the outcome of catalytic reactions by stabilisation of important reaction intermediates. Further studies of the alternative C4 activation of the azolium salts and use of related azoles show C4 activation and coupling may be possible, while the unactivated azoles are unlikely to be coupled using the same mechanism. (Abstract shortened by UMI.)

Cette these presente l'acces a de nouveaux complexes metal-hydrure (m=mo) et metal-carbene (m=mo, fe) en serie pentamethylcyclopentadienyle. Les composes metal-hydrure monosubstitues mo(c#5me#5)(co)#2(pr#3)h sont selectivement prepares par substitution directe d'un ligand carbonyle par une phosphine a partir du derive hydrure mo(c#5me#5)(co)#3h. La reduction des complexes cationiques |mp'l||pf#6| par lialh#4 conduit a des complexes metal-hydrure non- mono- ou di-substitues selon un mecanisme par transfert monoelectronique. Nous avons etabli sans ambiguite que la reduction initiale du complexe |mp'||pf#6| procedait via des especes monosubstituees a 19 et 17 electrons. Ces especes sont suffisamment stables pour subir une ou deux reactions de substitution selon vraisemblablement un mecanisme associatif avec formation d'un complexe intermediaire a 19 electrons. La synthese du premier complexe organo-fer chiral en serie pentamethylcyclopentadienyle a ligand carbenique a ete realisee par o-alkylation du complexe metal-formyle neutre fe(c#5me#5)(co)(pmeph#2)cho. Ce complexe precurseur a ete prepare et isole a basse temperature. La procedure employee s'est revelee efficace sur le plan synthetique et constitue une extension a la chimie du fer des travaux realises sur les complexes du molybdene

This work is mainly concentrated on the development of new versatile ligand based on N,N’-disubstituted-1,8-diaminonaphthalene (1,8-DAN) for main group chemistry. Therefore, our initial efforts were made on the design of new ligand scaffold by using 1,8-DAN. Following that, new ligand family supported by 1,8-DAN was applied as ligands to main group elements (B, Al, In, Ga, and C). Furthermore, six-membered ring carbenes which are derived from the reaction between N,N’-disubstituted-1,8-diaminonaphthalene and carbon are also investigated. In addition, the stable carbenes were implied as a new ligand system for palladium, leading to the formation of metal ligand complexes. Therefore, the synthesis and reactivity of these complexes are also reported. Chapter I gives an explanation on the basic concepts in terms of the ligand designs and reports the reasons why N,N’-disubstituted-1,8-diaminonaphthalene has been chosen as the framework of for these ligands. Chapter II presents the approach to synthesize ligands depending on the substitution. Regarding this, three methods were successfully used: reductive amination, application of acyl halide followed by reduction, and copper catalyzed C-N coupling reactions. Chapter III describes the reactions between the N,N’-disubstituted-1,8-diaminonaphthalene and main group elements B, Al, Ga, and In in 13 group. In this chapter, a variety of mononuclear and dinuclear complexes are investigated and fully characterized. Furthermore, some computational studies are also reported for the comparison with experimental results. Chapter IV deals with new ligand family, carbene, which is derived from N,N’-disubstituted-1,8-diaminonaphthalene. Therefore, not only fundamental concepts for the NHC (N-heterocyclic carbene) are discussed but also synthetic pathways are introduced. Moreover, interesting features of free carbene are presented as well. Chapter V reports the potential of this new carbene ligand family as ligands for transition metal compound, especially, Pd(II) compounds. Several different pathways for synthesizing the desired metal carbene complexes are presented.