Enantioselectivity of immobilized Mn-salen complexes: A computational study

We use molecular dynamic simulations to investigate the origin of enantioselectivity of an anchored Mn-salen complex in MCM-41. This study provides new insight into the steric effects that relate to choices of substrate and linker and to the interplay with mesopore confinement. Avnir's continuous chirality measure method is adopted to quantify the chirality content of the Mn-salen complex. We show that the immobilized linker influences the enantioselectivity of the catalyst due to the increasing chirality content of the Mn-salen complex. Simulations with docked olefin (beta-methyl styrene) suggest that cis- and trans-substrates have different level of asymmetric induction to the Mn-salen catalyst. A trans-substrate induces higher chirality to the immobilized Mn-salen complex than cis-olefin. We rationalize the importance of immobilization and show how it relates to the steric communication between the substrate and the Mn-salen complex. These results are important for the interpretation of the en anti oselectivity of immobilized organometallic catalysts in nanoporous materials. (c) 2006 Elsevier Inc. All rights reserved.