Reusable Ruthenium and Rhodium Catalyst-Organic Frameworks for Ester Hydrogenations and Enyne Cycloisomerizations.

摘要

A method was developed to immobilize and reuse a catalyst for the asymmetric cycloisomerization of enynes. Immobilization is achieved through use of metal containing monomers, which are reacted with a cycloolefin via an alternating ring-opening metathesis polymerization, assembling a three-dimensional catalyst-organic framework. For example, [RhCl((R)-5,5'-dinorimido BINAP)] 2 was copolymerized with cis-cyclooctene using trans-RuCl2(CHPh)(PCy3) 2 as a catalyst. After supporting the resulting framework on barium sulphate, silver(I) hexafluoroantimonate was added in the presence of enyne substrates to generate cationic rhodium(I) sites. These catalytic rhodium(I) sites catalyzed the asymmetric cycloisomerization of enynes, and afforded a maximum of 620 turnovers and >99% ee over the course of six runs. This catalyst was also used for batch reactions with turnovers as high as 800. The maximum number of turnovers reported in literature for a homogeneous non-tandem cycloisomerization reaction is ten.