Solid-phase media for use in heterogeneous catalysis: A new strategy for differentiating reactants based on sorption differences.

摘要

The work herein describes the use of highly crosslinked macroporous polymers for use in heterogeneous catalysis. The first part of this study includes an in-depth investigation into the variables that affect sorption-controlled partitioning of substrates. Maximum concentration enhancements are observed when polar organic compounds, capable of hydrogen bonding, partition from fluorous solvent mixtures, into polar, porous polymers. In general, the stronger the interactions between the compound and the polymer surfaces, the higher the concentration enhancements.; Efforts to harness the increased concentrations and translate them into rate enhancements are discussed. The first application explores hydrogenation reactions using a polymer immobilized rhodium catalyst. Rates of reactions ran under sorption-controlled conditions are higher compared to a non-sorbing system, although rate does not increase linearly with concentration enhancements. Efforts toward sorption-controlled rate increases in the thermal Diels-Alder reaction are also discussed.; Another sorption-controlled application is described that is not focused solely on rate enhancements. Rather, partitioning differences are used as a basis for the kinetic differentiation of molecules. The goal was to take two kinetically indistinguishable compounds, styrene and 3-formylstyrene, that had small, but measurable partitioning differences. Under homogeneous catalytic conditions these compounds display nearly identical reactivities. Under sorption-controlled conditions, however, 3-formylstyrene displays higher reactivities compared to styrene, which is attributed to its higher partitioning. Although the rate acceleration of 3-formylstyrene is small, it is the first example of a reaction using controlled sorption into macroporous polymers to selectively transform two kinetically indistinguishable substrates.; The final application described is a series of molecular imprinting experiments ran to examine the effect of pore size, and shape on the selectivity in the allylic alkylation reaction. The synthesis of a polymerizable tyrosine based dppe-derivative (P2) is described. A series of P2PdX 2 metallomonomers (X2 = (R)-BINOL, ( S)-BINOL, Cl2 and pi-1,3-Ph2-allyl +) are synthesized and incorporated into porous organic polymers (pEDMA), and the molecular imprinting effects on X2 ligand removal are investigated. What is apparent from these experiments is the necessity for the catalyst to have sufficient room in the active site (dictated by the size of the sacrificial ligand, X2) to accommodate the reactants necessary to accomplish catalysis.