Synthesis, Characterization, and Application of Pd(II)-NNN Pincer Complexes in Direct C–H Arylation of Heteroarenes with Aryl Bromides

We report the synthesis,
characterization, and catalytic
activity
of two new palladium(II) complexes featuring benzo[d]oxazol-2-yl-based pincer ligands, namely, [Pd(NNNmor)Cl]
(C1) [Pd(NNNpic)Cl] (C2), and
(where NNNmor = N-(2-(benzo[d]oxazol-2-yl)phenyl)-2-morpholinoacetamide) NNNpic = N-(2-(benzo[d]oxazol-2-yl)phenyl) picolinamide.
Structures of the ligands and the complexes were confirmed by FTIR,
NMR and high-resolution mass spectrometry (HRMS). Further, the molecular
structure of C2 in the solid state was confirmed by single-crystal
X-ray diffraction. The complex showed pincer coordination mode with
a distorted square planar geometry. The catalytic activity of these
Pd(II) complexes in the direct arylation of indazoles and other heteroarenes
with aryl bromides has been explored, with complex C2 exhibiting better reactivity compared to complex C1. Mechanistic investigations revealed that the catalytic pathway
involves a PdII–PdIV-PdII cycle.
The results are supported by DFT calculations.