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was found to reduce the PdII precursor by first forming a five-
membered palladacycle and then undergoing a C–C cleavage
and decarboxylation. The reactivity of the reduced Pd0 species
towards a typical cross-coupling reactant, 4-bromotoluene, was
examined and the catalytic competence was demonstrated.
These results explain the superior performance of pivalic acid
in phosphine-free direct C–H arylation reactions.
We acknowledge the financial support from the Institute for
Basic Science (IBS-R10-A1) in Korea and thank Dr. Tristan Tsai
Yuan Tan for invaluable comments to this work.
Scheme 2 Reactivity of the Pd0 generated in situ to 4-bromotoluene.
Conflicts of interest
terminal vinyl carbon was detected at d = 111.4 ppm in the
13C{1H} spectra, while the resonance of methyl carbons was
found at d = 24.5 ppm. The assignment of the 13C resonances
was confirmed unambiguously using 2D heteroatom correla-
tion NMR spectroscopy (see ESI†). Furthermore, the reported
direct C–H arylation condition (Table 1) employing potassium
carbonate and pivalic acid instead of sodium pivalate was
explored in N,N-dimethylformamide-d7 (DMF-d7) in the same
manner, while the reaction was carried out at 120 1C for 14 h.
There are no conflicts to declare.
Notes and references
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1
Analysis of the H NMR spectra of this system also displayed a
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Chem. Commun.
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