Metal-catalyzed functionalization of c-c bonds in four-membered rings.

En els darrers anys, la funcionalització catalítica d´enllaços C-C ha suscitat un gran interés, essent una de les disciplines amb més potencial en química organometàlica. Aquesta tesi doctoral es basa en el repte de dissenyar nous mètodes catalítics de functionalitazió d´enllaços C-C en anells de cuatre baules. Específicament, s´ha demostrat la viabilitat per preparar cetones γ-arilades via rotura d´enllaços C-C catalitzada per Pd en anells de tert-ciclobutanol utilitzant clorur d´aril i tosilats (Capítol 2). La transformació presenta una gran generalitat amb càrregues de catalitzador molt baixes. Tanmateix, s´ha trobat que fosfines riques en electrons i impedides estèricament permeten evitar processos destructius de β-eliminació d´hidrògen. Amb els precedents del capítol 2, s´ha extés satisfactòriament la generalitat de la reacció de rotura d´enllaços C-C d´anells de tert-ciclobutanol mitjançant l´acoplament amb haloacetilens per donar lloc a cetones amb grups alquins en posició γ (Capítol 3). Curiosament, els substituents del grup alquí tenen una gran influencia en la reacció. És certament remarkable l´interés potencial de la metodologia ja que els productes finals poden ser transformats fàcilment en productes d´alt valor afegit mitjançant reaccions d´acoplament creuat. Al Capítol 4, s´ha pogut extendre les metodologies de trencament d´enllaços C-C en anells de cuatre baules mitjançant el desenvolupament d´una metodologia catalitzada per Ni entre benzociclobutanones i diens per donar lloc a cicloadicions [4+4]. El mètode va mostrar una preferència específica per la formació d´anells de vuit baules respecte la formació d´anells de sis baules. Aquesta tesi doctoral també ha estudiat el disseny de metodologies de fixació de CO2 i formació d´enllaços C-F mitjançant activació catalítica d´enllaços C-C (Capítol 5). Tot i que no s´han trobat condicions de reacció òptimes, el nostre grup de recerca està actualment involucrat en el disseny de metodologies semblants i s´espera que aquesta recerca permeti el disseny de processos de fixació de CO2 i formació d´enllaços C-F mitjançant trencament C-C en un futur no molt llunyà.Recientemente la funcionalización catalítica de enlaces C-C ha suscitado un gran interés en la comunidad científica a pesar de los retos que conlleva. Esta tesis doctoral se ha basado en diseñar nuevos procesos catalíticos para la funcionalización de enlaces C-C en anillos de cuatro miembros. Específicamente, se ha demostrado la viabilidad de preparar cetonas con grupos arilo en posición γ usando precatalizadores de Pd para promover la rotura de enlaces C-C en anillos de tert-ciclobutanol utilizando cloruros de arilo y tosilatos como agentes arilantes (Capítulo 2). La transformación se caracteriza por su amplia generalidad y baja carga de catalizador. La selectividad de la reacción puede ser fácilmente controlada por la naturaleza del ligando, en la que fosfinas con grupos ricos en electrones y voluminosos dan los mejores resultados, evitando la β-eliminación de hidrógeno de las especies organometálicas intermedias. Considerando los precedentes del Capítulo 2, se ha extendido esta metodología al acoplamiento con haloacetilenos para preparar cetonas con grupos alquino en posición γ (Capítulo 3). Curiosamente, los substituyentes del grupo alquino juegan un papel fundamental en la reactividad, pudiéndose controlar mediante la utilización de un cierto ligando. En el Capítulo 4, se ha desarrollado una nueva transformación basada en una reacción catalizada por compuestos de Ni para efectuar la síntesis de anillos de ocho eslabones mediante una reacción formal de cicloadición [4+4] de benzociclobutanonas y dienos simples. Curiosamente, dicho método muestra una especial preferencia para formar anillos de ocho eslabones sobre los, a priori, anillos de 6 eslabones que son más estables termodinámicamente. En la presente tesis doctoral se ha estudiado también la viabilidad de llevar a cabo una fijación catalítica de CO2 y la formación de enlaces C-F mediante una rotura de enlaces C-C (Capítulo 5) aunque no se han encontrado las condiciones óptimas para llevar a cabo tales transformaciones.The means to promote catalytic C-C bond-functionalization has gained a considerable attention in recent years and probably can be considered one of the most challenging and vibrant subjects in organometallic chemistry. This PhD thesis deals with the design of new metal-catalyzed functionalization of C-C bonds in four-membered ring frameworks. Specifically, we have demonstrated the viability of preparing γ-arylated ketones via Pd-catalyzed cleavage of C-C bonds in tert-cyclobutanol using aryl chloride or tosylate counterparts (Chapter 2). The transformation possesses a wide substrate scope and remarkable low catalyst loadings. Selectivity was controlled by the ligand in which electron-rich and sterically-hindered phosphine ligands provided a unique reaction outcome that avoided the proclivity of alkyl metal species towards destructive β−hydride elimination. Prompted by the precedents in Chapter 2, we successfully extended the scope of the metal-catalyzed C-C bond-cleavage of tert-cyclobutanols by using halo acetylene counterparts giving γ-alkynylated ketones (Chapter 3). Interestingly, substituents on the alkyne motif showed a remarkable influence on reactivity. Of particular interest is the application profile of such methodology since γ-alkynylated ketones could promote consecutive metal-catalyzed transformations into valuable synthetic intermediates. In Chapter 4, we extended the interest for C-C bond-cleavage beyond the use of tert-cycñobutanols. Specifically, we developed a Ni-catalyzed C-C bond-cleavage event in benzocyclobutenones for preparing eight-membered rings via formal [4+4]-cycloaddition with dienes (Chapter 4). The method shows a specific preference for eight-membered rings over thermodynamically more stable six-membered rings. This PhD thesis has also studied the development of catalytic CO2 fixation and C-F bond-formation via C-C bond-cleavage (Chapter 5). While we have not found reaction conditions to effect the desired transformations, our research group is actively involved in related catalytic endeavors and it is expected that such research will shed light into the targeted CO2 fixation or C-F bond-forming reactions via C-C bond-cleavage

Mechanisms and Kinetics for Sorption of CO2 on Bicontinuous Mesoporous Silica Modified with n-Propylamine

We studied equilibrium adsorption and uptake kinetics and identified molecular species that formed during sorption of carbon dioxide on amine-modified silica. Bicontinuous silicas (AMS-6 and MCM-48) were postsynthetically modified with (3-aminopropyl)triethoxysilane or (3-aminopropyl)methyldiethoxysilane, and amine-modified AMS-6 adsorbed more CO(2) than did amine-modified MCM-48. By in situ FTIR spectroscopy, we showed that the amine groups reacted with CO(2) and formed ammonium carbamate ion pairs as well as carbamic acids under both dry and moist conditions. The carbamic acid was stabilized by hydrogen bonds, and ammonium carbamate ion pairs formed preferably on sorbents with high densities of amine groups. Under dry conditions, silylpropylcarbamate formed, slowly, by condensing carbamic acid and silanol groups. The ratio of ammonium carbamate ion pairs to silylpropylcarbamate was higher for samples with high amine contents than samples with low amine contents. Bicarbonates or carbonates did not form under dry or moist conditions. The uptake of CO(2) was enhanced in the presence of water, which was rationalized by the observed release of additional amine groups under these conditions and related formation of ammonium carbamate ion pairs. Distinct evidence for a fourth and irreversibly formed moiety was observed under sorption of CO(2) under dry conditions. Significant amounts of physisorbed, linear CO(2) were detected at relatively high partial pressures of CO(2), such that they could adsorb only after the reactive amine groups were consumed.authorCount :7</p

Ligand-Accelerated Pd-Catalyzed Ketone γ-Arylation via C–C Cleavage with Aryl Chlorides

A highly efficient Pd-catalyzed arylative ring expansion of cyclobutanols via C–C bond cleavage is presented. The method allows the coupling of aryl chlorides at low catalyst loadings with a wide range of functional groups and substitution patterns, thus constituting a straightforward alternative for preparing rather elusive γ-arylated ketones

Mechanisms and Kinetics for Sorption of CO₂ on Bicontinuous Mesoporous Silica Modified with <i>n</i>-Propylamine

We studied equilibrium adsorption and uptake kinetics and identified molecular species that formed during sorption of carbon dioxide on amine-modified silica. Bicontinuous silicas (AMS-6 and MCM-48) were postsynthetically modified with (3-aminopropyl)triethoxysilane or (3-aminopropyl)methyldiethoxysilane, and amine-modified AMS-6 adsorbed more CO₂ than did amine-modified MCM-48. By in situ FTIR spectroscopy, we showed that the amine groups reacted with CO₂ and formed ammonium carbamate ion pairs as well as carbamic acids under both dry and moist conditions. The carbamic acid was stabilized by hydrogen bonds, and ammonium carbamate ion pairs formed preferably on sorbents with high densities of amine groups. Under dry conditions, silylpropylcarbamate formed, slowly, by condensing carbamic acid and silanol groups. The ratio of ammonium carbamate ion pairs to silylpropylcarbamate was higher for samples with high amine contents than samples with low amine contents. Bicarbonates or carbonates did not form under dry or moist conditions. The uptake of CO₂ was enhanced in the presence of water, which was rationalized by the observed release of additional amine groups under these conditions and related formation of ammonium carbamate ion pairs. Distinct evidence for a fourth and irreversibly formed moiety was observed under sorption of CO₂ under dry conditions. Significant amounts of physisorbed, linear CO₂ were detected at relatively high partial pressures of CO₂, such that they could adsorb only after the reactive amine groups were consumed