Membrane occluded catalysts: a higher order mimic with improved performance

Abstract

A general method to immobilise homogeneous catalysts and to improve the performance of heterogeneous catalysts is discussed. The method consists in embedding the catalysts in hydrophobic PDMS (polydimethylsiloxane)-membranes. Inspired on a complete structural mimic of cytochrome P-450 up to the level of the membrane, this technique gives superior properties to the membrane resident catalyst. The scope and limitations of this method are discussed by two examples of heterogeneous catalysts, i.e., FePc-Y (iron phthalocyanine zeolite Y) and [Mn(bpy) 2] 2+-Y (manganese bis(bipyridyl) zeolite Y), and three examples of homogeneous complexes, i.e., FePc, Ru-binap ([2,2′-bis(diphenylphosphino-1,1′-binaphtyl]chloro( p-cymene)-ruthenium chloride) and the Jacobsen catalyst ( N,N′-bis(3,5-di- tert-butylsalicylidene)-1,2-cyclohexane-diamine manganese chloride). Due to changed sorption in the zeolites, catalyst activity is enhanced and deactivation is suppressed. Furthermore, the membrane incorporation makes the use of a solvent redundant. For homogenous complexes, this procedure represents a general method for heterogenisation. Moreover, the technique opens new ways in the field of oxidation chemistry, where solvents are necessary to homogenise reagents which usually differ in polarity.