The design, synthesis and application of two two solid-supported molecular catalysts for enantioselective reactions are reported. First, Ru(II)-salen bis-pyridine catalysts were immobilized on polymer and silica supports for the asymmetric cyclopropanation of styrene using ethyl diazoacetate. These catalysts were highly selective, giving good enantio and diasteroeselectivity, but deactivated with reuse. Consideration of potential deactivation pathways led to reaction protocols that could allow for recycle without any catalyst deactivation over multiple cycles.  The Ru complexes prepared on the polymer supports were more active and selective than those on silica supports. Additionally, longer, flexible linkers on the polymer supports were more enantioselective and diastereoselective compared to shorter linkers.1Complexes involving rhodium are also versatile catalysts for reactions of diazo compounds, and are active with a wider array of diazonium reagents. Among these catalysts, Rh2(S-DOSP)4 is generally the most used catalyst for a variety of transformations involving donor/acceptor carbenoid intermediates. Despite its synthetic utility, reports of efficient catalyst designs that allow for catalyst recycle are rare, yet the high cost of the precious metal suggests clear benefits of recycling and reuse. To this end, a silica supported dirhodium catalyst was developed with modification of one of the four DOSP ligands. When it was applied to a variety of dirhodium catalyzed reactions, the products could be obtained in similar yields and levels of enantioselectivity as for its homogeneous courterpart, Rh2(S-DOSP)4. More importantly, the silica supported catalyst could be recycled 5 times without significant loss of yield and enantioselectivity.2 References 1. C. S. Gill, K. Venkatasubbaiah, C. W. Jones, Adv. Synth. Catal. 2009 , 351, 1344-1354.2. K. Chepiga, Y. Feng, N. A. Brunelli, C. W. Jones, H. M. L. Davies, Org. Lett., 2013 , 15, 6136-6139

Polymer and silica supported Ru and Rh carbene catalysts for asymmetric olefin cyclopropanation and C-H activation

248th National Meeting (2014)

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