Supported ligands for metal catalyzed reactions

Identificador:  TDX:919

Handle: https://hdl.handle.net/20.500.11797/TDX919

Autors:  Marcos Escartín, Rocio

Resum:
Synthesis of homogeneous ligands and their use in catalysis constitutes one of the most important subjects in organic chemistry originating thousands of published works every year. From an industrial point of view, the application of such methodologies is rather limited due to the high cost of chiral ligands and noble metals used in such transformations. Moreover, sometimes the final products contain high levels of metal contamination, which can become a serious drawback if the metal is toxic. Strategies for immobilization of homogeneous catalysts onto bulk materials have been developed with the aim of combining the efficiency of homogeneous asymmetric catalysts with the easy separation, reuse and recycling of heterogeneous ones. An additional advantage of the immobilization approach is the possibility of implementing continuous flow processes. In this work, different approaches for the immobilization of the ligands onto polymers have been described. Thus, the effects of the spacer, the linker, the diverse resins and the different point of anchoring of ligands onto support have been evaluated for metal-mediated reactions. Additionally, recycling studies have been made with the best supported ligands. In order to demonstrate usefulness of the heterogenized ligands, we developed a continuous flow process using metal-supported catalyst in the asymmetric allylic amination. In the second part of the present thesis, we have evaluated the behaviour of different Lewis acids to induce stereospecific cyclizations from enantiomerically pure aryl glicidyl ethers. Through the research work herein described, we have demonstrated, contrary to previous claim about only gold mediating this reaction, Lewis acids do in fact catalyze this rearrangement. In particular, from the perspective of practical use, cost and availability considerations, FeBr3 (alone or in combination with silver triflate) can be considered as the reagent of choice for this operation and, in general, for processes where gold and other expensive metals merely act as simple Lewis acids. From a mechanistic point of view, the observed reactivity trends clearly indicate that these cyclizations are of the Friedel-Crafts type.