Bidding - the International Association of the Catalysis Societies

C&EN Volume 80, Number 26, p. 21 (July 1, 2002)
Suzuki coupling catalyzed by palladium shells
Hollow palladium spheres fabricated in the laboratory have been successfully used as a recyclable
heterogeneous catalyst for Suzuki coupling reactions [J. Am. Chem. Soc., 124, 7642 (2002)]. Taeghwan
Hyeon, an associate professor of chemical engineering at Seoul National University, in South Korea, and
coworkers prepared spherical shells that are 300 nm across and consist of 10-nm palladium particles. The
large surface area of these shells makes them highly active catalysts in Suzuki cross-coupling reactions
such as the one shown here. In previous studies, other groups reported that palladium nanoparticles used
in these reactions agglomerated after one cycle, resulting in a loss of catalytic activity. "To our surprise,"
Hyeon and coworkers write, "[our Pd spheres] maintained their catalytic activities even after seven
recycles. In addition, simple filtering can retrieve the catalyst from the reaction pot." Hyeon says this
heterogeneous catalyst is nearly as active as the most popular homogeneous palladium catalyst used for
Suzuki coupling. Furthermore, he believes the new catalyst could also be applied to other important
carbon-carbon coupling reactions.
C&EN Volume 80, Number 38, p. 90 (September 23, 2002)
Ionic liquid coating boosts biocatalysis
Biocatalysis in organic solvents, while convenient for process chemistry, generally limits the activity and
selectivity of enzymes that naturally operate under aqueous conditions. To compensate, enzyme
modification, molecular imprinting, and other approaches have been used to boost the efficiency of
enzymes. A new approach reported by graduate student Jae Kwan Lee and chemistry professor Mahn-Joo
Kim of Pohang University of Science & Technology, in South Korea, involves coating enzymes with an
ionic liquid [J. Org. Chem., 67, 6845 (2002)]. The researchers melt the imidazolium salt shown at 53 °C,
then add 0.1 mass equivalent of Pseudomonas cepacia lipase powder. This mixture is first stirred, cooled
to re-form a solid, and then broken down into small particles. Lee and Kim tested the ionic liquid-coated
enzyme in the transesterification of secondary alcohols in toluene. They found that the coated enzyme has
nearly the same activity as the untreated enzyme and in most cases provides a twofold improvement in
enantioselectivity.
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