Molecularly enlarged S,S-BnTsDPEN ligands for iron-catalyzed asymmetric olefin epoxidation reactions using hydrogen peroxideElectronic supplementary information (ESI) available: Experimental procedures and characterization data. See DOI: 10.1039/c3cy00484h

• Main Authors: Yazerski, Vital A, Orue, Ane, Evers, Tim, Kleijn, Henk, Klein Gebbink, Robertus J. M
• Format: Article
• ISSN: 2044-4753; 2044-4761
• DOI: 10.1039/c3cy00484h

A convenient approach for the anchoring of S , S -BnTsDPEN ligands ( S , S-N -tosyl-1,2-diphenylethylenediamine) to branched carbosilane scaffolds was investigated. It is based on a high-yielding reductive amination reaction between commercially available S , S -TsDPEN and readily accessible carbosilanes furnished with benzaldehyde terminal fragments. These molecularly enlarged ligands, bearing four S , S -BnTsDPEN units, and their simplified monomeric and "dimeric" analogues were evaluated in iron( iii )-catalyzed asymmetric trans -stilbene epoxidation reactions using hydrogen peroxide as an environmentally benign oxidant. The catalytic investigations showed a large degree of variation in the activity and stereoselectivity of the series of DPEN catalysts. In combination with ESI-MS investigations, these data revealed an important role of the ligand orientation in determining the overall activity of the catalyst system. Accordingly, a suitable design of the molecularly enlarged ligands resulted in fully retained activity and selectivity in catalysis. Finally, a number of strategies for the recovery and reuse of the best performing carbosilane-tethered DPEN ligands were explored. A series of structurally different carbosilane-supported TsDPEN ligands were found to display dramatically different activities and recyclabilities in the enantioselective epoxidation of stilbenes.