Tethered catalysts
المؤلف:
Peter Atkins, Tina Overton, Jonathan Rourke, Mark Weller, and Fraser Armstrong
المصدر:
Shriver and Atkins Inorganic Chemistry ,5th E
الجزء والصفحة:
719
2025-10-20
324
Tethered catalysts
Key point: The tethering of a catalyst to a solid support allows easy separation of the catalyst with little loss in catalyst activity. One popular technique has been the tethering of a homogeneous catalyst to a solid support. Thus, a hydrogenation catalyst such as Wilkinson’s catalyst can be attached to a silica surface by means of a long hydrocarbon chain:
When the silica monolith is immersed in a solvent, the rhodium-based catalytic site be haves as though it is in solution, and reactivity is largely unaffected. Separation of the products from the catalyst simply requires the decanting of the solvent. Commercially available functionalized silica precursors include amino-, acrylate-, allyl-, benzyl-, bromo-, chloro-, cyano-, hydroxy-, iodo-, phenyl-, styryl-, and vinyl-substituted reagents. Relatively simple reactions can result in the synthesis of a whole host of further reagents (such as the phosphine compound in the scheme above). In addition to silica, polystyrene, polyethene, polypropene, and various clays have been used as the solid support and have led to reports of the successful heterogenization of most reactions that rely on soluble metal complexes. In some cases the activity of a supported catalyst is greater than that of its unsupport ed analogue. This improvement normally takes the form of enhanced selectivity brought about by the steric demands of approaching a catalyst constrained to a surface or an increase in catalyst turnover frequencies brought about by protection from the support. Often, however, supported catalysts suffer from catalyst leaching and reduced activity.
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