Design and sinthesys of new gold, palladium and rhodium complexes with chiral ligands based on dioxolane and proton sponge backbone. Study of their heterogeneization and catalytic behavior

Resumen

In green chemistry, both homogeneous and heterogeneous catalysis have great importance in catalyzed processes that have several advantages with classical organic synthesis such as, shorter processes, high selectivity, less salts formation, milder reaction conditions and the use less hazardous solvents and reagents. Furthermore, in some cases catalytic processes need less steps leading to high productivity. Working lines in our research group are focus on the design and synthesis of new catalytic systems that can be supported (through modifications in the ligand) on inorganic matrix (mesoporous materials as MCM-41) and to induce chirality. The creation of an asymmetric environment around a metal center to accommodate the transformation of organic substrates, allows the induction of enantioselectivity in catalytic processes. A classical approach to achieve this goal is the use of enantiomerically pure ligands containing donor atoms (mainly nitrogen), with a defined symmetry. This project involves the design, preparation and evaluation of new gold (I), palladium (II) and rhodium (I) catalysts as soluble and MCM-41 supported forms, with particular attention on the role of the support on reactivity, enantioselectivity and recyclability in asymmetric hydrogenation reactions of pro-chiral succinates and multicomponent reaction for the synthesis of propargylamines. Thus, the goals of this thesis dissertation involves the synthesis of two families of chiral ligands with high capacity for coordination with transition metals (gold, palladium and rhodium) leading catalysts with high activity, enantioselectivity, and stability in the working conditions of catalytic tests, so they could be heterogenized and reused in successive reactions without loss of properties. N-heterocyclic carbene palladium (II), rhodium (I) and gold (I) complexes are based on a chiral dioxolane backbone, derived from optically pure tartaric acid (the backbone of the ligand is one of the key aspects to considered in the design of chiral ligands) the chiral dioxolane backbone supports groups that coordinate with the corresponding metal such as N-heterocyclic carbene groups or different amines, one of them is functionalized with isopropoxysilane groups for immobilization on MCM-41. In last years, the NHC's are becoming one of the real alternatives to phosphine-based catalysts with the promise of similar reactivity, greater efficiency, less toxicity, stability to air and more electronic and structural diversity. On the other hand, we synthesized a family of ligands based on a chiral proton sponge building block obtaining the corresponding palladium (II) and rhodium (I) complexes. The first example of a proton sponge (1,8-bis-(dimethylamino) naphthalene) was reported in 1968 by Alder but until now only one complex derived from diamine naphthalene proton sponge and only an example of chiral proton sponge reported by Mazaleyrat are known. We obtained two types of catalysts derived from this backbone, imino, and perimidine derivates. Imine catalysts could be supported on MCM-41 by functionalization of the ligands with triethoxysilane groups. All systems were tested as catalysts in asymmetric hydrogenation of pro-chiral succinates and multi-component reactions for the synthesis of propargylamines. Taking account activity and enantioselectivity and comparing with other catalysts available in the literature. For heterogenized catalysts we studied the role of the support in the activity and enantioselectivity in each model reactions and the possibility of recycling in successive reactions. For developed of the project the following stages took place: ¿ Design and synthesis of ligands: Proton sponge ligands are based on chiral 8-( (2R,5R)-2,5-dimethylpyrrolidin-1-yl)naphthalen-1-amine, in this molecule the two methyl groups of pyrrolidine are in anti configuration and they confer the ability to induce chirality. N-heterocyclic carbene ligands are based on the backbone of the molecule, (4R,5R)-4,5-bis (iodomethyl) -2,2-dimethyl-1 ,3- dioxolane. In this molecule the two iodines found in anti position, so if they are replaced by an SN2 reaction with other substituents these must also be in the same position. ¿ Synthesis of soluble and silyloxy palladium, rhodium and gold complexes. ¿ Immobilization on MCM-41. ¿ Study of activity and enantioselectivity in asymmetric hydrogenation reactions of pro-chiral olefins and multi-component reactions for the synthesis of propargylamines, emphasizing the difference between soluble and heterogenized catalysts and recyclability.