(Salen)nickel-catalysed epoxidations in the homogeneous and heterogeneous phase: The implications of oxygen on the efficiency and product selectivity

• Tipo: Artigo em Revista Científica Internacional
• Data: 2005

Autores

Ferreira, R (Autor) Outra; Garcia, H (Autor) Outra; de Castro, B (Autor) FCUP; Freire, C (Autor) FCUP

Revista

Título: European Journal of Inorganic Chemistry

Vol. 2005

Páginas: 4272-4279

ISSN: 1434-1948

Editora: Wiley-Blackwell

Indexação

ISI Web of Knowledge - 20 Citações

Scopus - 21 Citações

Classificação Científica

FOS: Ciências exactas e naturais > Química

Outras Informações

ID Authenticus: P-000-0HE

DOI: 10.1002/ejic.200500314

Abstract (EN): The catalytic activity of several nickel(II) complexes with salen-type ligands and their zeolite-immobilised analogues is assessed in the epoxidation of trans-beta-methylstyrene by NaOCI, in the absence and in the presence of oxygen. The complexes were immobilised in zeolites X and Y using the "ship-in-a-bottle" procedure, and the resulting materials were characterised by chemical analysis, XPS and IR, and UV/Vis diffuse reflectance spectroscopy. The loading and the distribution of the complexes in the materials were found to be dependent on the ligand. All (salen)nickel complexes proved to be active in the homogeneous and heterogeneous epoxidation of trans-beta-methylstyrene by NaOCl. The immobilised complexes gave lower conversions and their catalytic activity is dependent on the loading and distribution of the complexes within the zeolites. In both homogeneous and heterogeneous systems, the alkene conversion is influenced by oxygen. Removing oxygen from the reaction media results in lower alkene conversion but higher epoxide selectivity. Based on these results, two competitive mechanisms are proposed for the epoxidation reaction, one implying the formation of free radicals and other involving the binding of the substrate to a (oxo)metal intermediate. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005).

Idioma: Inglês

Tipo (Avaliação Docente): Científica

Nº de páginas: 8