abstract
The preparation of multipurpose asymmetric heterogeneous catalysts based on the immobilization of expensive privileged chiral ligands onto porous supports is essential for their use in industry. The benchmark cyclopropanation of styrene has been performed using a copper(II) complex of a commercial chiral bis(oxazoline) anchored onto ordered mesoporous silica materials (including SBA-15) and their carbon replicas (including CMK-3), and for the first time, we also report on the asymmetric aziridination of styrene by anchored copper(II) bis(oxazoline). All the composites prepared were active and enantioselective in these two organic transformations. In the cyclopropanation of styrene, the best heterogeneous catalyst gave higher enantioselectivities and TON than in the corresponding homogeneous phase reactions. In the aziridination of styrene the enantioselectivities for the best heterogeneous catalysts were similar to the propylated bis(oxazoline). The mesoporous silica, prepared by a straightforward one-pot procedure, was always among the best supports for the functionalized bis(oxazoline) in all the asymmetric processes studied. However its carbon replica was not a good support for the outcome of these asymmetric transformations, always yielding the lowest enantioselectivities. Once again the mesoporous materials surface properties were an important factor for the uniform distribution of the homogeneous catalyst, as well as for the course of the asymmetric organic reactions, together with the pore size. The best results presented herein are comparable to the ones reported for copper(II) bis (oxazoline) (2) immobilized onto other types of porous supports. (C) 2014 Elsevier Ltd. All rights reserved.
keywords
ASYMMETRIC HETEROGENEOUS AZIRIDINATION; CARBON REPLICAS; COMPLEXES; LIGANDS; SUPPORT; STYRENE; SILICAS; OLEFINS; IMMOBILIZATION; ADSORPTION
subject category
Chemistry; Crystallography
authors
Albuquerque, H; Carneiro, L; Carvalho, AP; Pires, J; Silva, AR
our authors
Ana Rosa Silva
Principal Researcher
Liliana Patrícia Teixeira Carneiro
Research FellowshipGroups
Projects
acknowledgements
This work was funded by the Fundacao para a Ciencia e a Tecnologia (FCT) through the project PTDC/QUI/64770/2006, which was co-financed by the EU under the programs COMPETE, QREN and FEDER. ARS thanks FCT, FSE and POPH for the contract under the programs Ciencia 2008 and Investigator FCT 2012 (IF/1300/2012), as well as for financing under the program Pest-C/CTM/LA0011/2013 (CICECO) and PEst-OE/QUI/UI0612/2013 (CQB/FC/UL).