Sistemas catalíticos para a metátese, carbonilação e hidrogenação de substratos de origem natural

Abstract

In the present work, catalytic methodologies were developed to transform naturally occurring olefins, such as 1-propenylbenzenes and β-pinene, into valuable molecules with potential use as agrochemicals, pharmaceutical precursors and monomers. These methodologies are based on ruthenium and rhodium catalyst to promote metathesis, hydroformylation, and hydroaminomethylation (HAM) reactions in homogeneous media. Also, catalytic methodologies of aldehyde hydrogenation and alcohol dehydration were developed using palladium, ruthenium, platinum and alumina catalyst in heterogeneous media. These processes were applied in tandem and one-pot methodologies. Initially, an estragole hydroformylation system was developed using the catalytic precursor Ru3(CO)12 as an alternative to the use of more expensive rhodium precursor. Reaction parameters such as temperature, pressure, phosphorus/Ru ratio, ligands and solvents, were optimized, obtaining yields of 71 % for aldehydes derived from estragole, with the preferential formation of linear aldehyde. In a second system, the cross-metathesis of naturally occurring 1-propenylbenzenes with ethylene gas (ethenolysis) was studied. By optimizing reaction parameters such as the nature of the catalyst, amount of catalyst, ethylene pressure, solvent and reaction time, yields of up to 99 % were obtained for functionalized styrenes, between these products are obtained 4-vinylanisole which has potential use as selective pesticide, and 4-vinylguaiacol used as flavor in industry. Once ruthenium-catalyzed hydroformylation and ethenolysis systems have been studied, a tandem assisted ethenolysis-hydroformylation catalytic system has been developed using a single ruthenium pre-catalyst. A one-pot system was also developed with ruthenium and rhodium catalytic precursors for ethenolysis – hydroformylation. The tandem and one-pot systems were applied to the selective transformation of 1-propenylbenzenes into α-arylaldehydes, molecules of interest as pharmaceutical precursors. With a one-pot approach, an ethenolysis-HAM system catalyzed by ruthenium and rhodium was developed for the selective transformation of 1-propenylbenzenes into arylethylamines with final yields up to 97 % for products with potential biological activities. Finally, an olefin homologation system for the diastereoselective synthesis of cis-vinylpinane from β-pinene was developed through hydroformylation, hydrogenation and dehydration reactions catalyzed by rhodium, platinum and alumina. The present work was structured in chapter’s format. In the introduction, the fundamentals of applied catalytic methodologies and their relation with green chemistry are described, next, the aims of the proposal are enunciated followed by the experimental chapter. The other chapters describe the catalytic methodologies applied, each one with a brief introduction of relevant references linked to the study proposal.