environmental and economical points of view, and various
strategies have been used to recover and recycle the
catalysts. One method involves the immobilization of
homogeneous catalysts on a solid support which usually
enables facile separation from the reaction mixture and
the possible recycling of the catalysts.6 Unfortunately,
heterogeneous catalysts prepared in this way are often
much less active than their homogeneous counterparts.
The search for superior catalysts that can combine the
advantages of both homogeneous and heterogeneous
catalysis remains a challenge to chemists.
Dendrimers have received considerable attention due
to their unique architectures and properties.7 One of the
most promising applications of dendrimers is their use
in catalysis.8 Because of the highly branched and well-
defined structure with multiple active sites, dendritic
catalysts offer potential in building a bridge between
homogeneous and heterogeneous catalysis.8b,d,e,9 Ex-
amples of the use of dendritic catalysts in organic
reactions include Kharash addition,8h,10 hydrogenation,9a,11
oxidation,12 Heck reaction,8g,13 Stille coupling, Knoevena-
gel condensation, Michael addition,14 and the asymmetric
addition of diethylzine to aldehydes.15 Recently, we
investigated the immobilization of dendritic ligands on
Ca r bon yla tive Rin g Exp a n sion of
Azir id in es to â-La cta m s w ith
Rh od iu m -Com p lexed Den d r im er s on a
Resin
Shui-Ming Lu and Howard Alper*
Centre for Catalysis Research and Innovation,
Department of Chemistry, University of Ottawa,
10 Marie Curie, Ottawa, Onterio, Canada K1N 6N5
halper@uottawa.ca
Received November 17, 2003
Abstr a ct: Rhodium-complexed dendrimers, supported on
a resin, were evaluated as catalysts for the carbonylative
ring expansion reactions of a variety of aziridines with
carbon monoxide to give â-lactams. The effects of reaction
temperature, solvent, time, and pressure of carbon monoxide
on this transformation were also investigated. The dendritic
catalysts showed comparable activity to the homogeneous
analogue. More importantly, this catalytic system can be
easily recovered by simple filtration and recycled without
significant loss of activity.
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10.1021/jo030353r CCC: $27.50 © 2004 American Chemical Society
Published on Web 04/21/2004
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