Desenvolvimento e avaliação de sistemas catalíticos heterogêneos para reações de acoplamento carbono-carbono de Suzuki-Miyaura

• Main Author: Souza, Guilherme Botelho Meireles de
• Publication Date: 2019
• Format: Master thesis
• Language: por
• Source: Repositório Institucional da UFG
• Download full: http://repositorio.bc.ufg.br/tede/handle/tede/9355
• topic: Paládio; Níquel; Nióbio; Catalisador suportado; Reação de acoplamento cruzado; Suzuki-Miyaura; Catálise Heterogênea; Palladium; Nickel; Niobium; Supported catalyst; Cross- coupling reaction; Suzuki-Miyaura; Heterogeneous catalysis; ENGENHARIAS::ENGENHARIA QUIMICA

Suzuki-Miyaura cross-coupling reactions are one of the most efficient and powerful tools for the formation of new carbon-carbon bonds, which have been widely applied in modern organic synthesis and industrial processes. Generally, these reactions are carried out by homogeneous catalysis, employing expensive palladium complexes such as PdCl2 associated with harmful phosphine ligands. However, these synthetic route presents several drawbacks such as high associated toxicity, catalyst recovery difficulties and waste disposal problems. In this context, several heterogeneous catalysts were proposed to overcome the great challenge of separation and recovery of homogenous catalysts. Also, a low-cost catalyst was presented as an alternative for the usage of palladium as the main Suzuki-Miyaura cross-coupling catalyst. Palladium, Nickel, Copper and Cobalt catalysts supported on niobium pentoxide (Nb2O5) were synthesized via wet impregnation method and tested for the Suzuki-Miyaura coupling reaction between phenylboronic acid and 4- bromoanisole. The catalysts were well characterized by scanning electron microscopy, N2 physisorption, X-ray diffraction, X-ray fluorescence, Thermogravimetry/Differential Thermal Analysis. Both Copper and Cobalt catalyst did not show any activity towards Suzuki- Miyaura cross-coupling reaction. Palladium catalyst resulted in high isolated yields (up to 91%) under optimized conditions. Satisfactory yields (up to 48%) were achieved employing the Nickel catalyst. Recycling tests were performed and significant loss in activity was observed after the first catalytic cycle, which can be attributed to catalyst loss during its retrieval by filtration between cycles, leaching of the active phase, in particular for Pd/Nb2O5 catalyst, or the poisoning by inorganic species (mostly potassium) on the spent catalyst’s surface.