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

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 degreesC) than for the homogeneous system (- 10 degreesC). 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. (C) 2003 Elsevier B.V. All rights reserved.