Diedrik Tas

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.

Novel catalytic membranes for selective reactions

A survey is given of the potentials of a new kind of catalytic membranes consisting of a catalyst that is immobilised in a dense polymer matrix. When homogeneous, catalytically active complexes are occluded, these membranes constitute a new way of heterogenation. In the case of solid state catalysts, these composite membranes can improve the activity of the catalyst by changing sorption or by allowing experimental set-ups in which solvents become redundant.

The immobilization of sulfonated Ru-BINAP chloride by anion exchange on layered double hydroxides

Summary A heterogeneous and enantioselective hydrogenation catalyst is developed, by anion exchange of sulfonated Ru-BINAP ([2,2′-Bis(diphenylphosphino-1,1′-binaphtyl]chlorobenzene-ruthenium (II)) chloride on the external surface of Layered Double Hydroxides (LDH). It is found by XRD that the binap-complex is only present at the outer surface and is not intercalated within the interlamellar space of the clay. The immobilized complex catalyses the hydrogenation of geraniol with good enantioselectivity. However, deactivation of the catalyst could not be avoided. The heterogeneous hydrogenation of dimethyl itaconoate proceeds at comparable rates and enantioselectivities than the homogeneous system, not showing deactivation. Leaching of the BINAP complex from the LDH surface was found to be absent in all cases.

Regio selectivity in the hydrogenation of geraniol over platinum containing zeolites

The hydrogenation of 3,7-dimethylocta-2,6-dien-1-ol (geraniol) ( 1 ) is performed over different platinum containing zeolitic materials such as beta, Y and MCM-41, prepared by impregnation with Pt(NH 3 ) 4 Cl 2 followed by drying, calcination and reduction. 3,7-dimethyl-6-octen-1-ol (citronellol) ( 2 ) and 3,7-dimethyl-2-octen-1-ol ( 3 ) are formed in different ratios, depending on the zeolite structure. The mechanism involved points to the existence of a tight host-guest interaction between the zeolitic voids and the substrate. Both shape selectivity and chemical properties of the zeolites play an important role in the induction of regio selectivity during reaction. It is found that geraniol can be converted selectively to citronellol by a proper combination of zeolite structure and metal cluster size.

Bifunctional catalytic membrane containing Brønsted acids and sites for enantioselective hydrogenation

The hydrogenation of methyl acetoacetate to give optically pure methyl 3-hydroxybutyrate is performed hetero-geneously with high activity and enantioselectivity under mild reaction conditions due to the combination of Bronsted acid and Ru–binap sites in a polydimethylsiloxane membrane matrix.

Homogeneous asymmetric hydrogenation ofo-chloroacetophenone to enantiomerically pureo-chloro-(1-phenyl)ethanol catalyzed by BINAP-Ru(II) complex

The BINAP-Ru(II) catalyst (2,2′-bis(diphenylphosphino)-1,1′-binaphthyl)chloro(p-cymene)rutheniun chloride is found to be highly active and enantioselective for homogeneous asymmetric hydrogenation of o-chloroacetophenone to optically pureo-chloro-(1-phenyl)ethanol. In contrast to results of Noyori and coworkers, no organic and inorganic bases are required to obtain high activities and enantioselectivities