No description available.

In the pursuit of increasingly efficient and/or new chemical transformations, homogeneous transition metal catalysts are proving to be invaluable components of the synthetic chemist’s toolbox. Notwithstanding the many important contributions made to the area of synthetic chemistry utilizing other transition metal catalysts, palladium-catalyzed cross-coupling techniques have been demonstrated to allow for a plethora of otherwise very difficult or even impossible bond forming reactions to be realized. In this context, appropriately designed ancillary ligands, which upon binding to a metal center can influence metal-centred reactivity, have played an essential role in the advancement of palladium-catalyzed cross-coupling reactions. This thesis describes a multi-faceted approach to the identification of effective ligands for the palladium-catalyzed construction of (sp2)carbon-nitrogen and -oxygen bonds. A new series of P,O-DalPhos ligands were developed and applied in the synthesis of of N-substituted indoles via tandem palladium-catalyzed cross-coupling/cyclizations of ortho-alkynylhalo(hetero)arenes with primary amines. Notably, one P,O-DalPhos variant, OTips-DalPhos, was demonstrated to offer the broadest known substrate scope in this important class of transformations, affording a variety of structurally diverse indoles and related heterocyclic derivatives in high yields. Also described herein is the identification of the previously reported ligand BippyPhos as an extremely robust and versatile ligand in both palladium-catalyzed carbon-nitrogen and -oxygen cross-coupling applications. Indeed, the use of a Pd/BippyPhos catalyst enabled the cross-coupling of a range of (hetero)aryl (pseudo)halides with primary and secondary amines, NH heterocycles, amides, ammonia and hydrazine, with representative examples being accommodated in air. The unprecedented scope of the Pd/BippyPhos catalyst in carbon-nitrogen cross-coupling allowed for the development of two novel one-pot, two-step syntheses of N¬-aryl heterocycles from ammonia, ortho-alkynylhalo(hetero)arenes and (hetero)aryl halides through tandem N-arylation/hydroamination reactions. A marked selectivity profile was also observed for the Pd/BippyPhos catalyst and successfully exploited in the chemoselective monoarylation of substrates featuring two distinct and potentially reactive NH-containing moieties. Finally, Pd/BippyPhos mixtures served as robust and efficient catalysts for the hydroxylation of a range of (hetero)aryl halides and ortho-alkynyl(halo)heteroarenes to form phenols and phenol-derived heterocycles.

Reaction of unsymmetrical allylic electrophiles with amines gives rise to regioisomeric allylamines. It was found that linear products result from the thermodynamically controlled isomerization of the corresponding branched products, which form initially. The isomerization was found to be promoted by the presence of acid and active palladium catalyst. The use of base shut down the isomerization pathway and allowed for the preparation and isolation of branched allylamines. This methodology provides a powerful control element, which allows for the installation of quaternary and chiral centres next to nitrogen. Later, the isomerization was combined with ring-closing metathesis to afford the synthesis of exocyclic allylamines from their thermodynamically less-stable endocyclic precursors. This rearrangement became feasible as a result of the electrophilic nature of a C – N bond in allylamines. When compared to the conventional intramolecular allylic amination, such approach escapes chemoselectivity issues, which makes it attractive attractive for late-stage synthetic modifications.

El objetivo de este trabajo se centró en la síntesis de nuevos catalizadores homogéneos de paladio para la reacción de copolimerización de monóxido de carbono con estireno. El interés de esta reacción catalítica radica en las propiedades de los copolímeros a que da lugar, que son termoplásticos bio- y fotodegradables. La ventaja de usar catalizadores homogéneos para la copolimerización, respecto a la polimerización radicalaria, es que en los copolímeros obtenidos las moléculas de monóxido de carbono y estireno se encuentran insertadas de una manera perfectamente alternada y regular. Para ello la utilización de precursores organometálicos de paladio(II) que posean un ligando quelato, ha sido descrita como la mejor forma de obtener sistemas activos.La influencia de la naturaleza del ligando quelato en la actividad del precursor catalítico, en especial la de sus átomos dadores, ha llevado a la elección de ligandos bidentados nitrógeno- y azufre-dadores para la realización de este trabajo. Así se ha escogido una serie de ligandos ditioéter, previamente utilizados en otros procesos catalíticos, así como ligandos piridina-pirazol y pirimidina-pirazol para estudiar su efecto sobre el metal y sobre la actividad del catalizador en la reacción de copolimerización. Además con el objeto de hacer un estudio sistemático de la influencia del ligando se ha diseñado y sintetizado una nueva familia de ligandos nitrógeno-dadores piridina-imidazolina de simetría C1. Estos nuevos ligandos piridina-imidazolina poseen la ventaja de ser fácilmente modificables, dando lugar a series de ligandos con variaciones estructurales sistemáticas.La coordinación de todos estos ligandos a paladio ha dado lugar a nuevos complejos neutros de fórmula [PdClMe(L-L)] y catiónicos de fórmula [PdMe(NCMe)(L-L)][X]. El análisis de la estereoquímica de los nuevos complejos sintetizados se realizó por RMN, observándose claras diferencias en función de ligando utilizado. Asimismo en algunos de los casos la obtención de monocristales ha hecho posible el análisis de la estructura en estado sólido de algunos de estos complejos, mediante difracción de rayos-X. La utilización de los complejos catiónicos de fórmula [PdMe(NCMe)(L-L)][BAr'4] como precursores de catalizador para la reacción de copolimerización ha dado lugar a la obtención de sistemas activos, de los que pueden extraerse las siguientes conclusiones:Los complejos de paladio que contienen ligandos ditioéteres son activos como precursores de catalizador para la reacción de copolimerización de 4-tert-butilestireno con monóxido de carbono, como se explica en el Capítulo 3. Sin embargo, los complejos son poco estables en atmósfera de CO, reduciéndose a paladio metálico. Los copolímeros obtenidos con estos catalizadores presentan microestructuras muy variables dependiendo del ligando azufre-dador utilizado. Se han podido obtener copolímeros isotácticos escogiendo el ligando ditioéter con la rigidez del esqueleto y con el tamaño de quelato apropiados, concretamente con el ligando (-)-deguspri.El Capítulo 4 describe la síntesis de nuevos complejos catiónicos de Pd(II) que contienen ligandos nitrógeno-dadores derivados del pirazol. La utilización de estos ligandos planos lleva a la obtención de complejos muy activos en la reacción de copolimerización, debido a sus propiedades estéricas y electrónicas. El estudio de la actividad de los precursores catalíticos y del peso molecular de los copolímeros obtenidos, en función del tiempo de reacción ponen de manifiesto que se trata de sistemas de polimerización "living". Los polímeros obtenidos son, en todos los casos, de elevado peso molecular y sindiotácticos.La síntesis de los nuevos ligandos nitrógeno-dadores derivados de la imidazolina, que poseen variaciones estructurales sistemáticas, se presenta en el Capítulo 5. La coordinación de estos ligandos a paladio ha dado lugar a complejos neutros [PdClMe(N-N')] que presentan la misma estereoquímica independientemente del ligando utilizado. Algunos de estos complejos han sido analizados en estado sólido por difracción de rayos-X.Se han observado diferencias en las distancias de coordinación del ligando al metal, en función del substituyente que posea la imidazolina en el nitrógeno amínico. Los complejos catiónicos sintetizados presentan, en disolución, notables diferencias estereoquímicas en función de la basicidad de los ligandos nitrógeno-dador utilizados. Así pues se han obtenido selectivamente estereoisómeros en función del ligando utilizado. La actividad de estos complejos catiónicos como precursores catalíticos para la reacción de copolimerización se ha observado que depende,fundamentalmente, de la basicidad del ligando, siendo más activos los catalizadores que poseen coordinados los ligandos menos básicos. En función del precursor utilizado es posible la síntesis de copolímeros con distinto grado de estereoregularidad. Así, precursores que poseen ligandos con substituyentes en el nitrógeno amínico que retiran densidad electrónica dan lugar a copolímeros sindiotácticos. En el caso de que los ligandos posean substituyentes dadores de densidad electrónica no se ha podido establecer una relación directa entre el precursor y la tacticidad del polímero. El estudio de la reactividad de los precursores catalíticos con CO ha sido realizada "in-situ" por RMN y ha puesto de manifiesto que los complejos formados son acilos-carbonilos de paladio de fórmula [Pd(COMe)(CO)(N-N')][X].Los precursores de catalizador que contienen ligandos nitrógenodadores,derivados tanto del pirazol como de la imidazolina, han resultado ser activos en la reacción de terpolimerización de tert-butilestireno y etileno con monóxido de carbono. Las diferencias estructurales de los ligandos utilizados tienen una marcada influencia en la reactividad de los complejos de paladio con los distintos alquenos. Ésto ha llevado a la obtención de terpolímeros con diferente concentración de monómeros en función de las propiedades estructurales del ligando nitrogenado utilizado. / The development and study of new palladium catalysts for the copolymerization of 4-tert-butylstyrene with carbon monoxide was the main objective in the present thesis. The role played by the chelating ligands and in particular by their donating atoms is known to be fundamental in this catalytic process and therefore sulfur and nitrogen-donating ligands were studied. As a result from this study, the following conclusions can be drawn:The new palladium(II) neutral and cationic complexes containing bis(thio)ethers as chelating ligands, synthesized in Chapter 3, show different behavior in solution depending on the rigidity of the ligand. The cationic complexes are precursors for the copolymerization of CO/4-tertbutylstyrene although they are quite unstable under carbon monoxide pressure and get reduced to inactive palladium metal. By choosing chiral bis-(thio)ethers with the appropriate backbone rigidity, good stereocontrol of the styrene insertion in the polyketone chain may be obtained.In Chapter 4 the coordination of a family of Cs-symmetrical pyrazolcontaining bisnitrogen ligands to palladium-methyl cationic complexes leads to different stereoisomers depending on the steric hindrance of the bisnitrogen ligand. They behave as active precursors for the copolymerization reaction and allow the synthesis of syndiotactic polyketones, irrespectively of the stereochemistry of the precatalyst. Under mild copolymerization conditions the pyrazol-containing catalysts are an example of living copolymerization catalysts.Chapter 5 deals with the synthesis of new chiral N1-substituted imidazolines which allow tuning the electronic properties of the metal to which they are coordinated. The differently substituted C1-symmetrical pyridine-imidazolines may lead to the selective synthesis of palladium cationic stereoisomers depending on the basicity of the ligand. Similarly under carbon monoxide atmosphere, palladium-acyl stereoisomers may be selectively obtained. When the different stereoisomers are used as precatalysts for the copolymerization of CO and 4-tert-butylstyrene, polyketones with different degrees of stereoregularity may be obtained.The combination of a pyridine or pyrimidine ring with a 5-membered nitrogen containing heterocycle (pyrazol or imidazoline) leads to effective achiral or chiral ligands, respectively, for the CO/4-tertbutylstyrene copolymerization and also CO/ethene/4-tert-butylstyrene terpolymerization reactions, as shown in Chapter 6. The palladium precatalysts with pyrazol-containing ligands are more stable under co- and terpolymerization conditions than the imidazoline-derived ones. The steric hindrance caused by the chiral imidazoline ligands may be responsible for the low reactivity of the palladium species towards 4-tert-butylstyrene,while the insertion of ethylene is more favored. This reactivity is reversed when less steric hindered nitrogen ligands are used.

Reaction of unsymmetrical allylic electrophiles with amines gives rise to regioisomeric allylamines. It was found that linear products result from the thermodynamically controlled isomerization of the corresponding branched products, which form initially. The isomerization was found to be promoted by the presence of acid and active palladium catalyst. The use of base shut down the isomerization pathway and allowed for the preparation and isolation of branched allylamines. This methodology provides a powerful control element, which allows for the installation of quaternary and chiral centres next to nitrogen. Later, the isomerization was combined with ring-closing metathesis to afford the synthesis of exocyclic allylamines from their thermodynamically less-stable endocyclic precursors. This rearrangement became feasible as a result of the electrophilic nature of a C – N bond in allylamines. When compared to the conventional intramolecular allylic amination, such approach escapes chemoselectivity issues, which makes it attractive attractive for late-stage synthetic modifications.

No description available.

The major part of this thesis concerns the development of catalytic methodologies based on palladium nanoparticles immobilized on aminopropyl-functionalized siliceous mesocellular foam (Pd0-AmP-MCF). The catalytic activity of the precursor to the nanocatalyst, PdII-AmP-MCF is also covered by this work. In the first part the application of Pd0-AmP-MCF in Suzuki-Miyaura cross-coupling reactions and transfer hydrogenation of alkenes under microwave irradiation is described. Excellent reactivity was observed and a broad range of substrates were tolerated for both transformations. The Pd0-AmP-MCF exhibited high recyclability as well as low metal leaching in both cases. The aim of the second part was to evaluate the catalytic efficiency of the closely related PdII-AmP-MCF for cycloisomerization of various acetylenic acids. The catalyst was able to promote formation of lactones under mild conditions using catalyst loadings of 0.3 - 0.5 mol% at temperatures of up to 50 oC in the presence of Et3N. By adding 1,4-benzoquinone to the reaction, the catalyst could be recycled four times without any observable decrease in the activity. The selective arylation of indoles at the C-2 position using Pd-AmP-MCF and symmetric diaryliodonium salts is presented in the third part. These studies revealed that Pd0-AmP-MCF was more effective than PdII-AmP-MCF for this transformation. Variously substituted indoles as well as diaryliodonium salts were tolerated, giving arylated indoles in high yields within 15 h at 20 - 50 oC in H2O. Only very small amounts of Pd leaching were observed and in this case the catalyst exhibited moderate recyclability. The final part of the thesis describes the selective hydrogenation of the C=C in different α,β-unsaturated systems. The double bond was efficiently hydrogenated in high yields both under batch and continuous-flow conditions. High recyclability and low metal leaching were observed in both cases. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: Submitted. Paper 5: Submitted.</p><p> </p>

The regioselectivity in Pd(0)-catalyzed direct arylation of pyrrole, thiophene, and indole can be improved by blocking some of the reactive sites with a chloride group, leading to increased yields of the desired regioisomers. Competition experiments and computational studies show that the blocking group also activates the substrates toward arylation. Due to the activated nature of chlorinated heteroaromatics, rare and sought after regioisomers, such as 3-arylthiophenes, can be obtained under mild conditions in good yields. Chlorine-bearing thiophenes arylated at C3 and C4 have the potential to undergo controlled regioregular polymerization under conditions developed in the field of polythiophene chemistry. Mechanistic studies support the hypothesis that the arylation of the substrates under investigation likely proceeds via the CMD transition state.

The development of new, improved methods for forming carbon–carbon and carbon–heteroatom bonds is the basic goal in synthetic organic chemistry. In the Lautens group, many recent advances have been made using late transition metals such as rhodium and palladium. One such research project involves the synthesis of indoles through tandem C–N and C–C coupling reactions using gem-dibromoolefin starting materials, and this area serves as a starting point for the research described. Chapter 1 describes a method by which the tandem use of gem-dibromoolefins can be halted to give intramolecular monocoupling reactions, maintaining one of the carbon–bromine bonds which can serve as a useful handle for further functionalization. The use of copper as a catalyst is key to this reaction, as it features a unique mechanism for carbon–heteroatom bond formation. Benzofurans and benzothiophenes can be prepared by this method. Chapter 2 describes the synthesis of 2-bromoindoles using an intramolecular Buchwald–Hartwig amination of gem-dibromoolefins. It is found that the products are more reactive towards palladium(0) than the starting material, and the use of a bulky phosphine ligand which facilitates reversible oxidative addition is required. This represents one of the first catalytic applications of this step in synthesis. Chapter 3 further explores the concept of reversible oxidative addition in a novel carbohalogenation reaction of alkenes. Aryl iodides tethered to alkenes are treated with a palladium(0) catalysts, which can undergo the basic steps of oxidative addition, carbopalladation, and novel sp2 carbon–iodine reductive elimination. This process is remarkably simple in concept, and is a waste-free, atom economically method for preparing new carbon–carbon bonds. Chapter 4 discusses various limitations to the carbohalogenation methodology, and seeks to overcome these problems. The use of aryl bromide starting materials can be accomplished by adding an iodide source to the reaction, allowing halide exchange of palladium(II) intermediates to occur. Intermolecular and asymmetric variants are also explored. Computational studies are discussed which reveal useful mechanistic details of the catalytic cycle, and this information is used in the development of novel phosphine ligands.

The regioselectivity in Pd(0)-catalyzed direct arylation of pyrrole, thiophene, and indole can be improved by blocking some of the reactive sites with a chloride group, leading to increased yields of the desired regioisomers. Competition experiments and computational studies show that the blocking group also activates the substrates toward arylation. Due to the activated nature of chlorinated heteroaromatics, rare and sought after regioisomers, such as 3-arylthiophenes, can be obtained under mild conditions in good yields. Chlorine-bearing thiophenes arylated at C3 and C4 have the potential to undergo controlled regioregular polymerization under conditions developed in the field of polythiophene chemistry. Mechanistic studies support the hypothesis that the arylation of the substrates under investigation likely proceeds via the CMD transition state.