Encapsulation of Transition Metal Catalysts
A R T I C L E S
based on palladium(II) ions and 1,3,5-tris(4-pyridylmethyl)-
benzene.15 Interestingly, these trinuclear cages assemble in high
yields in the presence of a suitable guest molecule as template
for the reaction (i.e., sodium p-methoxybenzoate). Metal-ligand
interactions between a guest template and structurally self-
complementary bisporphyrins also lead to the formation of
molecular capsules enclosing multidentate coordinating spe-
cies.16
quinone and 1,3-cyclohexadiene resulted in a rate acceleration
when carried out inside self-assembled glycoluril-based cap-
sules.20 Metallocages have been shown to be also suitable as
microreaction vessels, and various reactions taking place inside
this type of supramolecular structures have been reported.21 An
early example comes from the group of Sanders, who used
trimeric zinc(II) porphyrin architectures as templates for the
preorganization of substrates that result in more efficient acyl
transfer reactions22 or lead to unusual Diels-Alder adducts.23
Many reactions of interest require the use of well-defined
transition metal catalyst, but general techniques to encapsulate
such catalysts have not been reported yet. Here, we report such
a general strategy that involves the assembly of simple building
blocks as zinc(II) porphyrins24,25 and pyridylphosphines,26
leading to encapsulated transition metal catalysts.27 The forma-
tion of these encapsulated transition metal catalysts leads to a
One of the interesting functions of molecular capsules
involves their use as unique microreaction chambers, which can
lead to stabilization of highly reactive species17 or enhanced
reaction between two simultaneously bound substrate mol-
ecules.18,19 For example, a Diels-Alder reaction between 1,4-
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