Effect of Nanospace Confinement on the Catalytic Activity and Stability of a Chiral Schiff Base Complex (CuL; L=C22H24N2O4): A Combined Experimental and Theoretical Study. Issue 3 (27th January 2014)

• Record Type: Journal Article
• Authors: Bania, Kusum K.; Karunakar, Galla V.; Sarma, Bipul; Deka, Ramesh C.
• Is Part Of: ChemPlusChem. Volume 79:Issue 3(2014:Mar.)
• Page Start: 427
• Page End: 438
• Publication Date: 2014-01-27
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1002/cplu.201300432
• Languages: English
• ISSNs: 2192-6506

Abstract

<abstract abstract-type="main" xml:lang="en"> <title>Abstract</title> <p>Emerging trends in recyclable homogeneous chiral catalysts and their application in asymmetric synthesis are prompting a renewed interest in the field of catalysis as well as in industry. However, owing to fatal disadvantages of the homogeneous catalyst, they are not easily recoverable and recyclable. Herein, a comparison is made of the recyclability and stability of a homogeneous chiral Cu<sup>II</sup> Schiff base complex of general formula Cu<bold>L</bold>, in which <bold>L</bold>=C<sub>22</sub>H<sub>24</sub>N<sub>2</sub>O<sub>4</sub>, with that of a zeolite‐Y‐confined heterogeneous catalyst. On the basis of our experimental evidence, we demonstrate how self‐decomposition and bimetallic formation disrupt the catalytic activity of a homogeneous catalyst. By exploiting the special structure of faujasite zeolite, self‐decomposition of the chiral catalyst is fully controlled and efficiently used for the asymmetric nitroaldol reaction. The use of ionic liquid results in catalytic enhancement and provides a convenient way to recycle the homogeneous catalyst up to three cycles. When encapsulated in a cavity of faujasite by means of the "ship‐in‐a‐bottle" synthesis method, it shows much better catalytic activity with enhanced enantioselectivity, recyclability, and stability. The heterogeneous catalyst is recycled up to nine cycles and retains the catalytic activity for a longer period of time relative to its homogeneous counterpart. The synthesized heterogeneous Cu<sup>II</sup> complex provides the nitroaldol product with a maximum of 84 % yield and 87 % enantiomeric excess (<italic>ee</italic>; <italic>R</italic> isomer). Structural and reactivity differences between the homogeneous and heterogeneous chiral complexes are substantiated by density functional theory (DFT) calculations.</p> </abstract>