Demonstration of a zeolite effect on an encapsulated Co-salen-complex

• Published in: Journal of molecular catalysis. A, Chemical Vol. 206; no. 1; pp. 253 - 259
• Main Authors: Möllmann, Eugen, Tomlinson, Petra, Hölderich, W.F
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.10.2003; Elsevier
• Subjects: Catalysis; Catalysts: preparations and properties; Chemistry; Co-salen-complex; Conformation; Exact sciences and technology; General and physical chemistry; Ion-exchange; Simulation; Surface physical chemistry; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Transhydrogenation; Zeolites; Zeolites: preparations and properties; Co-salen-complex; Simulation; Zeolites; Transhydrogenation; Conformation; Encapsulation; Cobalt Complexes; Transition metal Complexes; Zeolite; Ketone; Molecular sieve; Heterogeneous catalysis; Acetophenone; Benzenic compound
• ISSN: 1381-1169; 1873-314X
• DOI: 10.1016/S1381-1169(03)00372-8

Extensive molecular dynamics simulations of a Co-salen-complex captured inside a zeolite matrix showed, that due to the zeolite the complex prefers a distorted conformation which is preserved in course of the simulations at different temperatures and that the zeolite is able to confine the occluded complex to this conformation even at higher temperatures. In a transhydrogenation, acetophenone was converted to 1-phenylethanol over a Co(II)-salen-complex entrapped in a USY-zeolite. This catalyst was prepared via “ship in the bottle”-method. The hydrogenation in the presence of this immobilized Co(II)-salen-complex results in an enantiomeric excess as high as obtained over the homogeneous complex. High e.e.-values were obtained over the immobilized catalyst at higher temperatures (25 °C) than for the homogeneous system (−10 °C). From these experimental results, it is assumed that the zeolite favors a certain structure of the occluded salen-complex and preserves this conformations at elevated temperatures. By computer simulation, it could be illustrated that due to the interaction of the homogeneous catalyst with the zeolite the complex prefers a distorted conformation. This conformation is preserved in course of the simulations at different temperature, i.e. the probabilities of finding the observed angles inside a given interval around the most probable angle are higher for the occluded complex than for the free one.