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58
59
Figure 16.29 Depropargylation of 58 forms fluorescent complex 59.
Adapted from Ref. 85.
(a)
60
61
(b)
51
52
53
Figure 16.30
(a) Pd-catalyzed cyclization of non-fluorescent aryl iodide 60 generates
fluorescent product 61. (b) Compound 53 was subjected to palladium
analysis.
Reproduced with permission from Ref. 86. Copyright 2010 American
Chemical Society.
16.4.2.5 Chemodosimeters Based on Cross-Coupling Reactions
Ahn's group used an intramolecular Buchwald-Hartwig-type cyclization
[Figure 16.30(a)] to convert the non-fluorescent rhodamine derivative 60 to
the fluorescent rhodamine derivative 61.
86
Although platinum and iron
catalyzed this fluorimetric conversion to some extent, palladium was by far
the most ecient. They applied this method to quantify palladium in 53,
prepared by a Suzuki-Miyaura coupling [Figure 16.30(b)].
86
After each of the
three rounds of purification, the palladium concentration was 10.2 ppm, 960
ppb and 110 ppb, respectively.
86
These values are unusually low compared
with typical palladium contents reported by pharmaceutical companies (see
above). Unfortunately, their data were not compared with those produced by
other analytical methods, such as ICP-MS, to validate their method. In
addition, their reported lower concentrations appear to be below the limit of
quantification. Compound 60 was colorless, whereas 61 was red, making
this method chromogenic.
Although the Heck reaction has potential to be used in the development of
chemodosimeters for palladium, thus far there is only one report in the
literature. Hong and co-workers used N-methylpyridinium unit 62 and aryl
bromide 63 to form the green fluorescent product 64 catalyzed by Pd(OAc)
2
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