Heck coupling in zeolitic microcapsular reactor: A test for encaged quasi-homogeneous catalysis

A new strategy of heterogenizing homogeneous catalysts by encaging the quasi-homogeneous catalytic reaction into a zeolitic microcapsular reactor has been proposed. As an example toward achieving such goal, a highly stable, nanopalladium-entrapped zeolitic microcapsular reactor (Pd@S1) was successfully fabricated and evaluated for Heck coupling reaction. The Pd@S1 not only exhibits excellent reactivity at low Pd adoption (Pd/PhI = 0.0025) during the reaction, but also can be reused for more than 10 runs with negligible loss of activity, in contrast to rapid decay of activity of conventional Pd/C catalysts. Such reusability can be explained by the encapsulation of the quasi-homogeneous reaction mechanism of Heck coupling within the micrometer-sized hollow cavities of Pd@S1, which successfully avoids the Pd leaching during the reaction. The strategy may be helpful in the design of reusable, highly efficient catalysts with advantages deriving from both homogeneous and heterogeneous catalysts. (c) 2006 Elsevier Inc. All rights reserved.