Enantioselective Addition of Malonates and β‐Keto Esters to Nitroalkenes over an Organonickel‐Functionalized Periodic Mesoporous Organosilica
A periodic mesoporous organosilica (PMO) with chiral cyclohexyldiamine‐based nickel(II) complexes incorporated within the silica framework was prepared through a co‐condensation of (1R,2R)‐cyclohexyldiamine‐derived silane and Ph‐bridged silane followed by complexation of nickel(II) bromide in the presence of (1R,2R)‐N,N′‐dibenzylcyclohexyldiamine. Structural analyses by X‐ray powder diffraction, nitrogen sorption and transmission electron microscopy disclosed its orderly mesostructure while characterization by solid‐state NMR and X‐ray photoelectron spectroscopy demonstrated the well‐defined single‐site chiral bis(cyclohexyldiamine)‐based nickel(II) active centers incorporated within the PMO material. In particular, as a heterogeneous chiral catalyst, this periodic mesoporous organosilica showed high catalytic activity and excellent enantioselectivity in asymmetric Michael addition of 1,3‐dicarbonyl compounds to nitroalkenes (more than 92% conversions and up to 99% ee values). More importantly, this heterogeneous catalyst could be recovered easily and reused repeatedly nine times without obviously affecting its ee value, showing good potential for industrial applications.
Document Type: Research Article
Affiliations: Key Laboratory of Resource Chemistry of Ministry of Education, Shanghai Key Laboratory of Rare Earth Functional Materials, Shanghai Normal University, Shanghai 200234, People's Republic of China, phone: (+86)-21-6432-1819, Fax: (+86)-21-6432-1819
Publication date: November 26, 2012