resumo
A copper(II) chiral bis(oxazoline) homogeneous catalyst (CuBox) was anchored onto mesoporous materials using three procedures: method 1, first anchoring of the bis(oxazoline) functionalized with 3-iodopropyltrimethoxysilane onto hexagonal mesoporous silica, SBA-15 and silica gel and then copper(II) coordination; method 2, anchoring of the CuBox functionalized with 3-iodopropyltrimethoxysilane onto hexagonal mesoporous silica. SBA-15 and silica gel; and method 3, first anchoring onto silica gel of 3-iodopropyltrimethoxysilane and then anchoring of the CuBox. In methods 1 and 3, the remaining free silanol groups of the silica materials were also capped using trimethylsilane groups. The bis(oxazoline) ligand was also encapsulated onto copper(II) exchanged zeolites NaY and NaUSY as a simpler strategy for the homogeneous catalyst immobilization, method 4. The materials were characterized by ICP-AES, elemental analyzes, C-13 and Si-29 MAS NMR, FTIR, thermogravimetry and nitrogen adsorption at -196 degrees C. The materials were tested as heterogeneous catalysts in the benchmark reaction of cyclopropanation of styrene to check the effect of the immobilization strategy on the catalytic parameters as well as on their reutilization in several catalytic cycles. (C) 2012 Elsevier Inc. All rights reserved.
palavras-chave
ENANTIOSELECTIVE CATALYSIS; ASYMMETRIC CYCLOPROPANATION; MESOPOROUS MATERIALS; CHIRAL CATALYSTS; COMPLEXES; EPOXIDATION; AZIRIDINATION; BISOXAZOLINES; CONFINEMENT; STYRENE
categoria
Chemistry; Science & Technology - Other Topics; Materials Science
autores
Silva, AR; Albuquerque, H; Borges, S; Siegel, R; Mafra, L; Carvalho, AP; Pires, J
nossos autores
Ana Rosa Silva
Investigador Principal
Luís Mafra
Investigador PrincipalProjectos
agradecimentos
This work was funded by Fundacao para a Ciencia e a Tecnologia (FCT) through the Project PTDC/QUI/64770/2006, which was co-financed by EU under the Programs COMPETE, QREN and FEDER. A.R.S. thanks FCT, FSE and POPH for the contract under the Program Ciencia 2008. L.M. and R.S. acknowledge FCT for funding to the Project PTDC/QUIQUI/100998/2008; for supporting the Portuguese National NMR Network (RNRMN) and for the post-doc Grant SFRH/BPD/44355/2008. FCT is also acknowledged for funding under the programmes Pest-C/CTM/LA0011/2011 (CICECO) and PEst-OE/QUI/UI0612/2011 (CQB/FC/UL).