Recoverable, Soluble Polymer-Supported Organic Catalysts
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tivity, and productivity. The stability of the catalyst and the possibility
of an easy separation and maybe recycling are also important aspects to
be considered for an industrial asymmetric catalytic process.
In this context immobilization of the catalytic species on a solid support may represent a solution to some of the problems; not only the
recovery and the possible recycling of a catalyst may be investigated
and successfully realized through its immobilization, but also the studies of other issues such as stability, structural characterization and catalytic behaviour may be better conducted on a supported version of the
enantioselective catalyst.
These general considerations are true also for organic catalysts which
have recently been the subject of incredibly intense research activity
(Dalko and Moisan 2004). Today it is safe to state that a very high
number of fundamental organic reactions that once required the use of
metal-based enantiopure catalysts can now be performed, at an equal
level of chemical and stereochemical efficiency, by using substoichiometric amounts of structurally simple organic molecules. In this context, the term ‘organic’ is synonymous of ‘metal-free’ with all the advantages of performing a reaction under metal-free conditions. These
advantages might include, inter alia, the possibility of working in wet
solvents and under an aerobic atmosphere, dealing with a stable and
robust catalyst and avoiding the problem of a (possibly) expensive and
toxic metal leaching into the organic product.
Furthermore, as mentioned before, organic catalysts may be ready
immobilized on a support with the aim of facilitating catalyst recovery
and recycling (Benaglia et al. 2003).
It is reasonable to suppose that a simple organic compound will be
less affected by the connection to a support than a more structurally
complex and somehow more ‘delicate’ enzyme. Metal-free catalysts are
also more readily amenable than organometallic catalysts to anchoring
on a support in order to easily separate the product from the catalyst, and
to recover and recycle the latter. Indeed, it has repeatedly been shown
that the use of a metal-based catalyst immobilized on a support is often
problematic because of possible, extensive metal leaching and requires
catalyst regeneration by metal replenishment before recycling.
301
tivity, and productivity. The stability of the catalyst and the possibility
of an easy separation and maybe recycling are also important aspects to
be considered for an industrial asymmetric catalytic process.
In this context immobilization of the catalytic species on a solid support may represent a solution to some of the problems; not only the
recovery and the possible recycling of a catalyst may be investigated
and successfully realized through its immobilization, but also the studies of other issues such as stability, structural characterization and catalytic behaviour may be better conducted on a supported version of the
enantioselective catalyst.
These general considerations are true also for organic catalysts which
have recently been the subject of incredibly intense research activity
(Dalko and Moisan 2004). Today it is safe to state that a very high
number of fundamental organic reactions that once required the use of
metal-based enantiopure catalysts can now be performed, at an equal
level of chemical and stereochemical efficiency, by using substoichiometric amounts of structurally simple organic molecules. In this context, the term ‘organic’ is synonymous of ‘metal-free’ with all the advantages of performing a reaction under metal-free conditions. These
advantages might include, inter alia, the possibility of working in wet
solvents and under an aerobic atmosphere, dealing with a stable and
robust catalyst and avoiding the problem of a (possibly) expensive and
toxic metal leaching into the organic product.
Furthermore, as mentioned before, organic catalysts may be ready
immobilized on a support with the aim of facilitating catalyst recovery
and recycling (Benaglia et al. 2003).
It is reasonable to suppose that a simple organic compound will be
less affected by the connection to a support than a more structurally
complex and somehow more ‘delicate’ enzyme. Metal-free catalysts are
also more readily amenable than organometallic catalysts to anchoring
on a support in order to easily separate the product from the catalyst, and
to recover and recycle the latter. Indeed, it has repeatedly been shown
that the use of a metal-based catalyst immobilized on a support is often
problematic because of possible, extensive metal leaching and requires
catalyst regeneration by metal replenishment before recycling.