Protective Encapsulation of Acid-Sensitive Catalysts Using Polyethylene Ligands
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abstract
The stability of polyethylene oligomer (PE Olig)-entrapped salen-metal complexes toward acidolysis is described. These complexes dissolve in hot toluene and precipitate as hydrophobic powders. The salen species in these precipitates or in precipitates of admixtures of oligomeric complexes and unfunctionalized polyethylene are stable to acid when suspended in acidic methanol for 24 h at 25C. The lack of metal leaching due to acid-promoted demetalation was determined using both colorimetric and ICP-MS analyses. The ICP-MS results showed the amount of metal loss for PE Olig-salen-metal complexes was 0.27%, 0.45%, and 0.79% for half-salen Cr(III), salen Cr(III), and salen Mn(III) complexes, respectively. These results were in contrast to the reported behavior of low molecular weight salen metal complexes and to results seen with a salen complex bound to divinylbenzene (DVB) crosslinked polystyrene which demetalates under acidic conditions at room temperature. Salen complexes formed with PE Olig complexes also demetalate when the PE Olig-bound species are in solution at elevated temperature and exposed to acid. These results show that as solids oligomeric polyethylene ligands even without added PE can serve as a protective encapsulating matrix for the solid forms of polymer-supported catalysts. 2012 Wiley Periodicals, Inc.
