This thesis describes the synthesis, characterisation and reactivity of new manganese and rhenium(I) NHC complexes, which have been investigated both thermally and photochemically and the results contrasted with existing phosphine analogues in the literature. Cp’Mn(CO)2(NHC) (NHC = IEt2Me2 1, IMes 2, IiPr2Me2 3 and IPr 4) were synthesised and investigated by TRIR spectroscopy. Loss of CO was observed after 355 nm irradiation to form agostically stabilised intermediates, which reformed the parent species by recombination with CO on the nanosecond timescale. Loss of NHC was not observed, in contrast to Cp’Mn(CO)2(PPh3) which lost both CO and PPh3 upon photolysis. [Re(NHC)(Bpy)(CO)3]BAr4F (NHC = IEt2Me2 5, IMes 6) were synthesised and investigated by TRIR spectroscopy and UV/Vis absorption and emission spectrometry. Inclusion of an NHC altered the excited state manifold of the complexes, favouring population of the 3MLCT over the 3IL excited state. The lowest energy excited state for both 5 and 6 proved to be a 3MLCT excited state at 298 and 77 K. In contrast, [Re(PPh3)(Bpy)(CO)3]BAr4F exhibited 3MLCT at 298 K, but 3IL at 77 K. A series of complexes, M(NHC)(CO)4X and M(NHC)2(CO)3X (M = Re, X = Cl; M = Mn, X = Br) formed upon reaction of the corresponding M(CO)5X species and free NHC. The substitution pattern was dictated by the steric bulk of the NHC. Generation of the corresponding cations by halide abstraction was investigated. M(NHC)2(CO)3X was found to form agostic stabilised species upon halide abstraction by NaBAr4F in CH2Cl2. Under the same conditions, Re(IPr)(CO)4Cl was found to form the dichloromethane complex, [Re(IPr)(CO)4(η1-CH2Cl2)]BAr4F. In C6H5F solution under an atmosphere of dihydrogen, the CH2Cl2 ligand could be displaced by H2 to form the dihydrogen species, [Re(IPr)(CO)4(H2)]BAr4F.

The palladium-mediated cross-coupling of aryl electrophiles and amines (Buchwald-Hartwig amination) has become a widely used method of constructing arylamine frameworks. A crucial aspect of the advancement of this chemistry has been the design of ancillary ligands that are able to promote enhanced reactivity in challenging amination reactions. Despite significant ligand development within the field, challenges in this chemistry remain. Chemoselective aminations, wherein one amine substrate undergoes preferential arylation in the presence of multiple reactive amines has remained an underexplored area of Buchwald-Hartwig amination chemistry. This thesis describes the use of [Pd(cinnamyl)Cl]2 and N-[2-di(1-adamantylphosphino)phenyl]morpholine (Mor- DalPhos) in an extensive study of chemoselective Buchwald-Hartwig aminations, with 62 examples of structurally diverse di-, tri-, and tetraamines obtained in synthetically useful yields at reasonable catalyst loadings (1-5 mol % Pd). The coordination chemistry of [(Mor-DalPhos)Pd] species was also explored, as were complementary chemoselective aminations with the isomeric p-Mor-DalPhos ligand, leading to divergent product formation in some instances. The same [Pd(cinnamyl)Cl]2/Mor-DalPhos catalyst system used in the chemoselectivity study was also employed in a series of Buchwald-Hartwig aminations conducted under aqueous and solvent-free conditions, another underexplored area of this chemistry. A total of 52 amine products were isolated using these methodologies, moderate catalyst loadings (3 mol % Pd), and without the use of any additional additives, co-solvents, or rigorous exclusion of air. The synthesis of low-coordinate palladium complexes featuring both NHC and dialkylchlorophosphine ligands is also discussed herein. These complexes are prepared via a previously unreported and straightforward methodology involving an unusual net PCl bond reductive elimination, and represent a potential new class of pre-catalysts forpalladium-mediated reactions.

The side-on dioxygen adducts of N-heterocyclic carbene (NHC) containing rhodium complexes, [ClRh(IPr)2(O2)] and [ClRh(IMes)2(O2)], previously synthesized in our laboratories possess a square planar geometry and O-O bond lengths of 1.323(3) and 1.341(4) Å, respectively. Both of these attributes are uncharacteristic of Rh(O2) complexes, which are typically octahedral and possess O-O bond lengths of approximately 1.45 Å. Full characterization by NMR, IR, Raman, DFT and XAS confirmed the short O-O bond lengths of these structures and revealed that they were rhodium(I) coordination complexes of singlet oxygen with no net oxidation/reduction process having taken place. The unique bonding mode appears to result from the interaction of a filled Rh d orbital with one of the two degenerate O2 * orbitals, which causes splitting of the O2 * orbitals, favoring spin pairing in the O2 HOMO, and the inability of Rh to donate electron density to the empty * orbital. Initial investigations of these complexes as catalysts for the reduction and oxidation of C-O bonds, as well as singlet oxygen generation were also undertaken. Rh(IPr)2 coordination complexes of N2, H2 and CO were also synthesized and characterized by X-ray crystallography, NMR and elemental analysis. Interestingly, the addition of hydrogen gas to rhodium did result in oxidation of the metal. A Rh(NHC) complex featuring an anionic acetate ligand, [(AcO)Rh(IPr)(CO)2], was synthesized and characterized by NMR, IR and X-ray crystallography. This complex proved to be an effective catalyst for the regioselective hydroformylation of aliphatic and aromatic alkenes, which occurred without isomerization of the alkene. Initial rates of hydroformylation with our catalyst were compared to the chloride analogue, [ClRh(IPr)(CO)2], and demonstrated the beneficial nature of replacing the halide with a carboxylate ligand, which is less inhibiting of the reaction. The synthesis of a bifunctional hydrogenation catalyst featuring a protic-NHC was attempted by addition of benzimidazoles to [Cl2Ru(diphosphine)]. Although these attempts were unsuccessful, a large number of complexes of the formula [Cl2Ru(diphosphine)(-N3-benzimidazole)2] were synthesized and proved to be effective catalysts for the chemoselective hydrogenation of ketones versus alkenes. Use of chiral diphosphines and 1-triphenylmethylbenzimidazole yielded catalysts capable of producing secondary alcohols with moderate enantioselectivity. / Thesis (Ph.D, Chemistry) -- Queen's University, 2010-09-17 12:44:52.686

No description available.

Thesis advisor: Amir H. Hoveyda / Formation of C-C bonds is an invaluable tool for the construction of materials, pharmaceuticals, natural products, and the building blocks of life. Although great strides in this area have been made, there remain several limitations in regio-, site-, and enantioselective additions of carbon-based nucleophiles. Solving these challenges by expanding the scope, efficiency, and selectivity of alkyl, aryl, heteroaryl, vinyl, and alkynyl additions to carbon-based electrophiles is the topic of this dissertation. / Thesis (PhD) — Boston College, 2013. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

No description available.

N-heterocyclic carbenes (NHCs) can be used as ligands for organometallics complexes, which can then facilitate numerous catalytic applications, such as, C-H activation, small molecule activation and numerous materials applications. The use of anionically-tethered NHCs for usage with electropositive metals has been pioneered by the Arnold group within the last decade. This thesis describes the synthesis of both aryloxide- and amide-tethered NHC organometallic complexes of s-, p-, d- and f-block metals to provide a platform for small molecule activation. Once synthesised, the reactivity of some of these complexes were tested by reaction with CO2 with the aim of turning a molecule considered a harmful (environmentally), waste product into value added products, potentially providing an alternative fuel source. Chapter One introduces the use of anionically-tethered NHCs for use in a number of organometallic complexes as well as their current potential as catalysts for a number of important small molecules. This chapter focuses upon the differences between complexes tethered with anionic O, N, P, S elements, f-element NHC complexes and the use of d-block NHC complexes for catalysis. Chapter Two contains the synthesis and characterisation of a number of aryloxy-tethered NHC p-, d- and f-block organometallic complexes using the ligand H2(LArO R)2. The synthesis of SnII complexes including the synthesis of new ‘normal’ ‘abnormal’ complexes given enough steric bulk around the Sn centre due to the lone pair present in Sn complexes, preventing one of the ligands binding through the classical carbene position and therefore binding through the backbone C4 carbon. The synthesis of MII (Zn, Co and Fe) complexes to compare the solid-state structure and binding mode of the carbenes. The synthesis and characterisation of MIII (Ce and Eu) complexes to assess the solid-state structure and binding modes within f-bock complexes. Chapter Three investigates the reactivity of the MII complexes (Sn, Zn, and Fe) with CO2. Successful reactions were characterised using NMR and further treated with alkynes to target catalytic reactions. Chapter Four contains reactions to target a number of amide-tethered bis (NHC) s-, p-, d- and f-block organometallic complexes using the proligand, H4(LN Mes)Cl3. Deprotonation studies undertaken with a number of bases to give the MI (Li and K) salts and MII (Mg) salts and proved to be unsuccessful upon isolation. Reactions to synthesise the p-, d- and f-block complexes were then undertaken using in situ free carbene production as well as the attempted isolation of the free carbene, both of which also proved unsuccessful. Chapter Five provides an overall conclusion to the work presented in Chapters Two, Three and Four within this thesis. Chapter Six gives the experimental and characterising data for the complexes and reactions.

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).

With the ever expanding utility of transition metal catalysis, there has been a thrust both to develop catalysts with unique selectivites or activites, and to understand the factors which govern these characteristics at both a fundamental and practical level. Olefin metathesis has become an essential reaction for the synthesis of small molecules in addition to polymeric materials. We have pursued two distinct ligand classes based on diaminocarbenes with novel architectures to address specific limitations within this useful class of reactions: 1) limited access to polymeric materials with controlled microstructures and 2) poor stereoselectivity in Ru-catalyzed cross-metathesis (CM) reactions. Numerous phosphines and N-heterocyclic carbenes (NHCs) have been used as ligands for Ru metathesis catalysts, and the resulting activity is very sensitive to their steric and electronic nature. We envisioned that we could take advantage of this dependence by developing a catalyst with tunable ligand donicity. Redox-switchable ligands can lead to catalysts whose selectivity and/or activity are dependent upon the ligand oxidation state. Towards this purpose, we have developed a ligand which incorporates a 1,1’-disubstituted ferrocene moiety into the backbone of a diaminocarbene (FcDAC). Upon ligation of FcDAC to various transition metals, we were able to use cyclic voltammetry and a spectroelectrochemical FT-IR experiment to show electronic communication between FcDAC and the coordinated metal. We then pursued Ru metathesis catalysts incorporating these ligands. The ring-opening metathesis polymerization of 1,5-cyclooctadiene was studied using [(FcDAC)(PPh₃)Cl₂Ru=(3-phenylindenylid-2-ene)] as the catalyst. Chemical redox reactions were used to establish the ability of FcDAC to impart redox-tunable properties to Ru metathesis catalysts. A new ligand class pioneered in our group, N-aryl,N-alkyl acyclic diaminocarbenes (ADCs), was also studied in various Ru metathesis catalysts. To our delight, these catalysts showed lower E : Z ratios than analogous NHC ligands in two representative CM reactions. We also investigated the conformational diversity of these differentially substituted ADCs given their ability to rotate about their C–N bonds, in particular, to determine how this might influence their donicity. Complexes of the type [(ADC)Ir(COD)Cl] and [(ADC)Ir(CO)₂Cl] were studied, given the wealth of structural and spectral data available for analogous compounds incorporating related ligand classes. Different conformations resulted depending on the N-substituents and the nature of the metal complex. Interestingly, the electron donating ability of ADC ligands was found to depend on their conformation, as evidenced by FT-IR and cyclic voltammetry. This established a new avenue for tuning the donor properties of differentially substituted ADC ligands. The unique properties of these novel ligand classes were demonstrated in Ru metathesis catalysts. However, on a broader level, these ligands are expected to have utility in diverse catalytic applications. / text

In the last ten years, N-heterocyclic carbenes(NHCs) have gained tremendouspopularity, notably as highly versatile ligands for transition metals. Their strong -donatingproperties, associated with high steric hindrance, often impart enhanced stability and activity to a given metallic center. Two main successes of the NHCs in homogeneous catalysis are arguably the ruthenium-mediated olefin metathesis and the palladium-promoted crosscoupling reactions.In this work, we have studied the effect of N-heterocyclic carbenes as supporting ligands in well-defined complexes of palladium(II), gallium(III), and gold(I) that we used in homogeneous catalysis.Notably, we have synthesized, in very straightforward manners, two families of palladium compounds of formulae [(NHC)Pd(L)Cl], where L, which is a R-allyl or R-acac moiety, acts as a protecting shell for the catalytically active [(NHC)Pd0] species. Hence,upon activation under the reaction conditions, these new Pd complexes were found extremely active in the Suzuki-Miyaura, the Buchwald-Hartwig, and the -ketone arylation cross-coupling reactions. More precisely, the more active "R-allyl family" allowed for reactions to be performed with as low as 10 ppm of palladium.A series of [(NHC)GaCl3] complexes wa synthesized via a simple one-step procedure. The resulting unprecedented NHC-GaIII compounds were found extremely stable but showed only moderate activity in isomerization reactions.Demonstrating further the versatile application of NHCs in metal-based catalysis, wedeveloped several new catalytic transformations using [(NHC)AuCl] complexes. Hence,these pre-catalysts, activated in situ with a silver salt, proved to be excellent activators ofalkynes, allenes, and alkenes. This led to the development of efficient synthetically usefulprotocols, encompassing enyne cycloisomerization, indene cyclization,formation of conjugated enone, and allylic rearrangement.KEYWORDS gallium - gold - homogeneous catalysis - N-heterocyclic carbene - palladium 8 / En los últimos diez años, los carbenos N-heterocíclicos (NHCs) han ganado una granpopularidad, especialmente como ligandos versátiles de metales de transición. Su fuertecarácter −donor, asociado con su gran impedimento estérico, confieren a menudo unamayor estabilidad y actividad al centro metálico en cuestión. Los dos mayores éxitos de losNHCs en catálisis homogénea se encuentran, sin duda, en la metátesis de olefinas catalizadapor rutenio y en las reacciones de acoplamiento cruzado promovidas por paladio.En este trabajo, hemos estudiado el efecto de los carbenos N-heterocíclicos comoligandos en complejos bien definidos de paladio(II), galio(III) y oro(I), que hemos empleadoen catálisis homogénea.En particular, hemos sintetizado, de forma directa, dos familias de compuestos de paladio de fórmula general [(NHC)Pd(L)Cl] donde L, grupo R-alilo o R-acac, actúa como protector para las especies catalíticamente activas [(NHC)Pd0]. De hecho, tras la activaciónen las condiciones de reacción, estos nuevos complejos de paladio se mostraron extremadamente activos en las reacciones de Suzuki-Miyaura, de Buchwald-Hartwig y en la -arilación de cetonas. Más concretamente, la 'familia R-arilo', más activa, permitió llevar a cabo estas reacciones con tan sólo 10 ppm de paladio.Una serie de complejos [(NHC)GaCl3] fue preparada en una simple etapa. Los compuestos resultantes NHC-GaIII, sin precedentes en la literatura, se mostraron extremadamente estables pero sólo moderadamente activos en reacciones de isomerización.Con el fin seguir ampliando la gran aplicabilidad de los NHCs en catálisis conmetales, estudiamos varias nueva transformaciones utilizando los complejos [(NHC)AuCl].De hecho, estos pre-catalizadores, activados in situ con una sal de plata, demostraron ser excelente activadores de alquinos, alenos y alquenos. Esto llevó al desarrollo de protocolos eficientes, y sintéticamente útiles, tales como la cicloisomerización de eninos, la ciclación deindenos, la formación de enonas conjugadas, y reordenamientos arílicos.