Thesis advisor: Marc L. Snapper / Chapter 1. A Practical Synthesis of 3-Acyl Cyclobutanones by [2 + 2] Annulation. Mechanism and Utility of the Zn(II)-Catalyzed Condensation of alpha-Chloroenamines with Electron-Deficient Alkenes. We have developed a catalytic method for the synthesis of highly functionalized 3-acyl cyclobutanones which are useful building blocks for a variety of natural products. Methods for cyclobutanone synthesis have traditionally been limited to Lewis-acid promoted rearrangement of oxaspiropentanes or cyclizations of ketene and syntheses involving keteneiminium salts have required stoichiometric quantities of a Lewis acid. Furthermore, the mechanism for these types of cyclizations remains unknown. This portion of my research focused on an efficient, catalytic method for the synthesis of 3- acyl cyclobutanones and providing insight into the mechanism for cycloaddition. Chapter 2. Enantioselective Synthesis of Boron-Substituted Quaternary Carbons by NHC-Cu-Catalyzed Boronate Conjugate Additions to Unsaturated Carboxylic Esters, Ketones, or Thioesters. We have developed an enantioselective NHC-Cu-catalyzed conjugate addition of boronate esters to acyclic, trisubstituted alpha, beta-unsaturated carbonyl compounds. Enantioselective conjugate addition of a boronic acid pinacol ester through the use of bis(pinacolato)diboron [B2(pin)2,] to alpha, beta-unsaturated aliphatic and aryl esters promoted by 5 mol % of an NHC-Cu catalyst afforded tertiary beta-boryl carbonyls in high efficiency and enantioselectivity. Trisubstituted alpha, beta-unsaturated esters and thioesters were found to be reactive substrates in the presence of a stoichiometric quantity of methanol. Chapter 3. Metal-Free Catalytic C-Si Bond Formation in an Aqueous Medium and C-B Bond Formation in a Protic Medium. Enantioselective NHC-Catalyzed Silyl and Boryl Conjugate Additions to Cyclic and Acyclic alpha, beta-Unsaturated carbonyls. We have developed a method for enantioselective metal-free silyl conjugate additions through the use of dimethylphenylsilyl) boronic acid pinacol ester [PhMe2SiB(pin)] catalyzed by chiral N-heterocyclic carbenes (NHCs) in basic aqueous thf. Optimization of metal-free conditions demonstrated that the presence of water was required for high efficiency. alpha, beta-Unsaturated cyclic ketones and lactones were examined as substrates, and acyclic ketones, esters and aldehydes were also competent substrates for silyl conjugate addition. beta-Silyl carbonyls were isolated in up to >98% yield and >98:2 er. Chapter 4. Elucidation of Mechanism for Enantioselective NHC-Catalyzed Silyl Conjugate Addition. We propose a catalytic cycle for NHC-catalyzed enantioselective silyl conjugate addition. Mechanistic studies of NHC-catalyzed enantioselective silyl conjugate additions are presented. Optimization of conditions for an inefficient alpha, beta-unsaturated electron-deficient ketone provided insight into the roles for dbu and water. Kinetic data indicate that conjugate addition is first order in PhMe2SiB(pin) and carbene, and DFT calculations support the formation of an NHC-silyl anion as a reactive intermediate in the catalytic cycle. / Thesis (PhD) — Boston College, 2012. / Discipline: Chemistry.

Several new late transition metal complexes containing P-O and P-N ligands derived from 2-dicyclohexylphosphinoacetaldehyde were synthesized. A facile one-pot template method is used for the synthesis of P-N complexes, where the phosphine aldehyde and amine can undergo a condensation reaction to form a phosphine-imine metal complex in the presence of a metal precursor. Metal complexes with phosphino-enolate, imine, and oxime ligands are synthesized. Ni(II), Pt(II), Rh(I) and Ir(I) metal centres were investigated. The Rh(I) and Ir(I) complexes contain a 1,5-cyclooctadiene ligand, thus resembling Crabtree’s hydrogenation catalyst [Ir(COD)(py)(PCy3)][PF6]. These complexes are also active catalysts for olefin hydrogenation. Furthermore, the synthesis of a new chiral amine functionalized NHC ligand is explored, which has potential applications as a ligand in the metal-catalyzed enantioselective hydrogenation of polar bonds. This ligand is inspired by previous achiral hydrogenation catalysts reported by Morris et al. that displayed high activity for a variety of unsaturated substrates.

En aquesta tesi s'han sintetitzat macrocicles nitrogenats poliinsaturats de diferents mides i s'ha estudiat la seva reactivitat. S'han preparat macrocicles de quinze i setze baules triacetilènics i de quinze baules contenint dos triples i un doble enllaç a l'estructura. S'ha estudiat la ciclotrimerització [2+2+2] d'aquests macrocicles catalitzada per metalls de transició en dissolvents orgànics convencionals o en sals foses. S'han sintetitzat complexos de rodi contenint un lligand carbènic N-heterocíclic per tal d'utilitzar-los com a catalitzadors alternatius al complex de Wilkinson en les reaccions de ciclotrimerització dels macrocicles poliinsaturats i d'altres anàlegs oberts. Els complexos carbènics sintetitzats han presentat una eficiència lleugerament superior a la del catalitzador de Wilkinson. També s'ha iniciat un estudi mecanístic de la cicloisomerització d'aquests macrocicles induïda tèrmicament.Finalment, s'han preparat macrocicles de catorze i dinou baules contenint un nucli endiínic a més d'altres insaturacions i s'ha estudiat la corresponent ciclació de Bergman en estat sòlid. / In this work different sized polyunsaturated azamacrocicles were synthesized and their reactivity was studied. 15- and 16-membered triacetylenic macrocycles and 15-membered macrocycles containing two acetylenes and one olefin were synthesized. The transition metal catalyzed [2+2+2] cyclotrimerization of the polyunsaturated macrocycles was studied in organic solvents or molten salts. Rhodium complexes containing a N-heterocyclic carbene (NHC) ligand were prepared in order to be used as alternatives to the Wilkinson's catalyst in the cyclotrimerization reaction of the polyunsaturated macrocycles and other open-chained analogues. The yields were slightly higher to those previously obtained with the Wilkinson's catalyst, showing that NHC can be used as alternative ligands to the phosphanes.A mechanistic study of the thermally induced cycloisomerization of the above-mentioned macrocycles was initiated.Finally, 14- and 19-membered azamacrocycles containing an enediyne system and other unsaturations were synthesized and their solid-state Bergman cyclization was studied.

No description available.

Several new late transition metal complexes containing P-O and P-N ligands derived from 2-dicyclohexylphosphinoacetaldehyde were synthesized. A facile one-pot template method is used for the synthesis of P-N complexes, where the phosphine aldehyde and amine can undergo a condensation reaction to form a phosphine-imine metal complex in the presence of a metal precursor. Metal complexes with phosphino-enolate, imine, and oxime ligands are synthesized. Ni(II), Pt(II), Rh(I) and Ir(I) metal centres were investigated. The Rh(I) and Ir(I) complexes contain a 1,5-cyclooctadiene ligand, thus resembling Crabtree’s hydrogenation catalyst [Ir(COD)(py)(PCy3)][PF6]. These complexes are also active catalysts for olefin hydrogenation. Furthermore, the synthesis of a new chiral amine functionalized NHC ligand is explored, which has potential applications as a ligand in the metal-catalyzed enantioselective hydrogenation of polar bonds. This ligand is inspired by previous achiral hydrogenation catalysts reported by Morris et al. that displayed high activity for a variety of unsaturated substrates.

The fields of N-heterocyclic carbenes and homogeneous gold catalysis have experienced tremendous growth within the last two decades. In addition, the combination of these fields to give NHC-gold complexes has delivered superior stability and reactivity, allowing the isolation of new reactive species and a better understanding of the fundamental chemistry. The work presented in this thesis attempts to synthesise novel NHC-gold complexes and document their reactivities. The main themes discussed in this work are: (a) the understanding and avoidance of silver additives in gold-mediated transformations; and (b) the study of different NHCs to provide optimal sterics and electronics for a given application. In Chapter 2, the reported “Gold(I)-Mediated C-H Activation of Arenes” is investigated. The role of each additive is assessed, and in particular the reliance on silver salts is considered. An NHC ligand was used to stabilise reactive intermediates, which provided new insights into the function of the silver additive. Gold(I) hydroxides are repeatedly shown to be invaluable synthetic equivalents, as well as key intermediates in silver-free protocols. Chapter 3 details numerous attempts to synthesise [Au(OH)(NHC)] complexes that are stable, pure and in high yields. Chapter 4 documents the synthesis of gold species featuring the ITent family of NHC ligands. Their highly flexible steric bulk is investigated by crystallographic studies, and is believed to contribute to their relatively high stabilities. Chapter 5 describes the use of the newly synthesised [Au(OH)(NHC)] complexes to generate mono- and bifluoride species. The reaction conditions were then optimised in order to maximise yields and regioselectivities. Finally, Chapter 6 examines the use of NHC selenium adducts to measure the π-accepting ability of these ligands. These are then coordinated to gold, whereupon different geometries are observed depending on the nature of the NHC.

No description available.

Avec le développement des concepts de la chimie verte, il est devenu nécessaire de remplacer les métaux toxiques par des composés plus respectueux de l’environnement. Donneurs d’hydrogène pour des réactions radicalaires, les hydrures de trialkylétain sont encore très utilisés. Les NHC-boranes se sont révélés de bons remplaçants pour les réactions de désoxygénation. Cependant, les réactions de déshalogénation effectuées avec des NHC-boranes sont moins efficaces et il a fallu avoir recours au concept de catalyse à polarité inversée. Ces travaux ont été le point de départ de cette thèse où la synthèse de nouveaux NHC-boranes possédant une liaison B-S ou B-N est développée. L’étude des propriétés de ces nouveaux complexes a été effectuée et des applications en chimie organique et en science des polymères ont été trouvées. Par ailleurs, en vue d’étudier les effets polaires sur la formation et la réactivité des radicaux boryles, une nouvelle famille de carbène-boranes a été synthétisée. / Along with the development of green chemistry, it became necessary to avoid toxic metallic complexes in organic reactions and replace them by more sustainable compounds. An hydrogen donors for radical reactions, trialkylstannanes are still widely used. NHC-boranes seem to be good substitutes for deoxygenation reactions. However, dehalogenation reactions are less effective and polar reversal catalysis was used. This work was the starting point of this Ph.D thesis where the synthesis of new NHC-boranes bearing a B-S or B-N bound is developed. The study of the properties of these new complexes was performed and applications in organic chemistry as well as in polymer science were found. Besides, to study polar effects on the formation and on the reactivity of boryl radicals, a new family of carbene-boranes was synthesized.

Depuis les années 2000, le domaine de l’organocatalyse est en plein essor. Une vue d’ensemble des différents modes d’activation organocatalytique fera l’objet du premier chapitre. Malgré les avancées considérables faites dans l’activation par liaison covalente, particulièrement dans l’aminocatalyse par activation iminium, des progrès sont encore possibles au niveau de l’activité catalytique des organocatalyseurs. Une large partie du travail détaillé dans le deuxième chapitre concerne le design puis le développement de deux voies de synthèse permettant de préparer une nouvelle classe d’organocatalyseurs pour l’activation iminium ainsi que leurs tests d’activité catalytique. Enfin, le troisième chapitre est consacré à l’étude de réactions d’échange H/D organocatalysées par les carbènes N-hétérocycliques. / Since the begining of 2000, the field of organocatalysis has performed a lot of improvements. An overview of the different modes of activation of this field will constitute the first chapter. Despite the improvements in the domain of activation by covalent bond, specially for the iminium activation, some enhancements of the catalytic activity of organocatalysts are still possible. A major part of the work developped in the second chapter will be focused on the design then the synthesis of a new class of organocatalysts for iminium activation and their catalytic activity tests. Then the third chapter will be dedicated to the H/D exchange reactions organocatalyzed by N-heterocyclic carbenes.

No description available.