Polyolefin-supported recoverable/reusable Cr(III)-salen catalysts

摘要

The design of functional soluble polyolefins for use as supports for salen ligands and metal complexes is described. Examples and applications that use both polyisobutylene (PIB)-and polyethylene (PEOlig)-bound recoverable/recyclable salen ligands/metal complexes are detailed. In the case of using PIB as a support, the polymer-bound complexes can be recovered through the use of latent biphasic or a thermomorphic mixed solvent systems. In the case of PEOlig-supported complexes, the thermomorphic PE Olig-bound salen species can be dissolved in "hot" solvents and quantitatively recovered as solids upon cooling to room temperature. Both the PIB-and PEOlig-bound salen catalysts were shown to catalyze the ring-opening of epoxides with various nucleophiles. Both sorts of polyolefin-bound catalysts can be recycled and reused with no observed loss in activity. However, limitations of catalyst concentration make chiral versions of these complexes uncompetitive in comparison to conventional chiral salen catalysts that can be used in neat substrate at higher concentration to produce high enantioselectivity in the ring-opening products. The preparation of a PIB-bound "half-salen" catalyst was also briefly examined.