Organic Letters
Letter
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solution by ICP-MS. The palladium content of the reaction
mixture was found to be <250 ppb, demonstrating that very
little metal leached into the reaction medium. Combined with
the ease of removing the catalyst from the reaction mixtures,
this low level of palladium in the reaction mixture is an
improvement on the existing homogeneous catalyst for N-
chelation-directed C−H activation reactions.
To demonstrate that the trace palladium in the reaction
mixture is not the source of catalytic activity, a hot filtration
experiment was performed with benzo[h]quinoline (Table 1,
entry 5). After 10 min at 100 °C, the Pd(II)/MWCNT catalyst
was removed by hot filtration over Celite. Fresh substrate and
oxidant were added to the filtrate, which was reheated to 100
°C. No further conversion to product or catalytic activity was
observed in the filtrate in the absence of Pd(II)/MWCNT,
showing that the <250 ppb of residual Pd that remains in
solution is not adequate to catalyze the C−H activation
reaction.
In conclusion, we have demonstrated that solid-supported
Pd(II)/MWCNT can catalyze N-chelation-directed C−H to
C−OAc, C−OMe, C−Cl, and C−Br activation reactions. For
all of the C−H activation reactions examined, the solid-
supported catalyst demonstrated consistently higher turnover
frequencies than the reported homogeneous catalyst. The solid-
supported Pd(II)/MWCNT also offers the advantages of ease
of removal by filtration and low levels of residual palladium
metal contamination in the products. We are currently working
to optimize the reactions reported here as well as apply this
catalyst to other N-chelation-directed C−H activation reac-
tions.
ASSOCIATED CONTENT
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S
* Supporting Information
Figure S1, Tables S1 and S2, experimental procedures, and
spectral data. This material is available free of charge via the
AUTHOR INFORMATION
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Corresponding Author
Notes
The authors declare no competing financial interest.
A patent application is being filed for this work.
ACKNOWLEDGMENTS
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This work was supported by the VCU School of Pharmacy.
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