Organic Letters
Letter
The dimer is further reacted with BrettPhos to yield the
desired palladacycle in high yield. Preparation of 20 using 1
proceeded as described in the literature with similar yield and
purity. In contrast, when using 3 for the dimer formation, no
conversion of the starting material was observed. Although the
use of 2 resulted in the formation of 20, a lower yield (72%
overall) with significant unidentified impurities was observed in
both the intermediate and final products. Compound 20,
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1
synthesized using 2 gave several impurity peaks by H NMR
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1
complex H NMR spectra, although the complex was reported
to be catalytically active.5b We were unable to isolate the
impurity for unambiguous structural assignment. In addition,
the product yield for both steps was lower when 2 was used
instead of 1.
In conclusion, this study provides the first systematic
investigation of the reactivity of pure palladium acetate in
comparison to two common impurities, 2 and polymeric 3.
Although 3 was believed to be inactive, this study demonstrates
that at elevated temperatures and slightly modified reaction
conditions (e.g., addition of a ligand) it exhibits high levels of
reactivity similar to pure 1 in Buchwald−Hartwig, Suzuki−
Miyaura and Mizoroki−Heck cross couplings, and in a ketone
alpha-arylation example. However, there are exceptions; for
example, 3 is inferior for the synthesis of a palladacycle
precatalyst and in cross-coupling at reduced temperatures and/
or in the absence of a phosphine ligand. On the basis of these
differences in reactivity of 2 and 3, we recommend high purity
palladium acetate as a control catalyst when evaluating
commercial samples of palladium acetate to ensure reliable
and reproducible results.
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ASSOCIATED CONTENT
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(8) (a) Roper, M. Chem. Unserer Zeit 2006, 40, 126. (b) Eicken, K.;
̈
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* Supporting Information
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The Supporting Information is available free of charge on the
Experimental procedures and characterization data
including solid-state NMR and DFT calculations
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AUTHOR INFORMATION
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Corresponding Author
Notes
The authors declare the following competing financial
interest(s): High purity palladium acetate and palladium
pivalate are commercially available through JMCCT (www.
(16) Kinzel, T.; Zhang, Y.; Buchwald, S. L. J. Am. Chem. Soc. 2010,
132, 14073.
ACKNOWLEDGMENTS
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We acknowledge Dr. Nathan Barrow, JMTC Analytical,
Sonning, for useful discussion of the 13C solid-state NMR
results and Dr. Andrew DeAngelis, Research Scientist, JMCCT
(currently at DuPont) for useful technical discussion.
D
Org. Lett. XXXX, XXX, XXX−XXX