Ring-Opening Metathesis A Reusable Polymeric Asymmetric Hydrogenation Catalyst Made by Ring- Opening Olfein Metathesis Polymerization By Corbin K. Ralph, Okwado M. Akotsi, and Steven H. Bergens

What did they do? Made the first polymeric asymmetric hydrogenation catalyst via ROMP –These types of catalysts are of interest because they are thought to have favorable characteristics of recovery and reuse Usually synthesized using other types of reactions besides ROMP –Metal center often interferes with the reaction

How did they do it? First noticed what catalysts other people were creating with ROMP –Predominantly organic-based, but some metal-based polymeric catalysts –Ru, Mo, Pd, and Fe Decided to focus on Ru

What did they use? The Precursors –trans-RuCl 2 (Py) 2 ((R,R)-Norphos) As the monomer –trans-RuCl 2 (=CHPh)(PCy 3 ) 2 –trans-RuCl 2 (=CHPh)(PCy 3 )(NHC) Alkylidenes as catalysts

What did they use?

Why did they use them? trans-RuCl 2 (Py) 2 ((R,R)-Norphos) –Easily prepared –Contains no accessible donor atoms that may deactivate catalysts trans-RuCl 2 (=CHPh)(PCy 3 ) 2 and trans- RuCl 2 (=CHPh)(PCy 3 )(NHC) –Known catalysts developed by Grubbs

What did they try? Reacted the monomer with 5 mol % of each catalyst for 24 h (22 o C, CH 2 Cl 2 ) –Failed to produce a polymer –Models showed sever crowding would exist between adjacent active sites Needed to reduce the crowding –Too bulky

A Solution Decided to try using cyclooctene as a spacer monomer

Eureka! Added 1 equivalent of COE to solution –33% complete after 3 h 1 H NMR after 66% had reacted showed the degree of alternating growth was high As they increased the ratio of COE to original monomer, the rate increased –4:1 ratio, 12 times as fast

The Cycle

What did they do with it? Wanted to create a chiral hydrogenation catalyst Cross-linked the ends of the long-chain polymer using dicyclopentadiene Coated the catalyst as a thin film over BaSO 4 –Chose BaSO 4 as a support because it is inert and helps improve the mechanical stability

Results Used this catalyst to hydrogenate 1- acetonaphthone Ran for 2 h and compared to homogeneous run using the original monomer –Rate was ~40% the rate of the original monomer Showed low mass transport losses Isolated the catalyst via filtration and reused it 10 more times –No significant drops in enantiomeric excess (ee) or rate

Results ee obtained from using the original monomer was 48% S ee obtained from new catalyst was 83% S –Much better

In Conclusion… Important finding because it is a reusable catalyst and has good yields –Synthesized more directly than other catalysts To further explore this topic… –Figure out a monomer than doesnt require a spacer –Try different backbones (instead of BaSO 4 ) for the catalyst