Mono and Dinuclear Palladium Pincer Complexes of NNSe Ligand as a Catalyst for Decarboxylative Direct C−H Heteroarylation of (Hetero)arenes

Abstract

This report describes the synthesis of a new NNSe pincer ligand and its mono and dinuclear palladium(II) pincer complexes. In the absence of a base, a dinuclear pincer palladium complex (C1) was isolated, while in the presence of an Et3N base a mononuclear palladium pincer complex (C2) was obtained. The new ligand and complexes were characterized using techniques like 1H, 13C{1H} Nuclear Magnetic Resonance (NMR), Fourier Transform Infrared (FTIR), High‐Resolution Mass Spectrometry (HRMS), Ultraviolet–visible (UV‐Visible), and cyclic voltammetry. Both complexes showed pincer coordination mode with a distorted square planar geometry. The complex C1 has two pincer ligands attached through a Pd‐Pd bond in a dinuclear pincer fashion. The air and moisture‐insensitive, thermally robust palladium pincer complexes were used as the catalyst for decarboxylative direct C–H heteroarylation of (hetero)arenes. Among the complexes, dinuclear pincer complex C1 showed better catalytic activity. A variety of (hetero)arenes were successfully activated (48‐87% yield) using only 2.5 mol% of catalyst loading under mild reaction conditions. The PPh3 and Hg poisoning experiments suggested a homogeneous nature of catalysis. A plausible reaction pathway was proposed for the dinuclear palladium pincer complex catalyzed decarboxylative C‐H bond activation reaction of heteroarenes.

Macrocyclic Sulfur Ligand Stabilized Trans‐Palladium Dichloride Complex: Syntheses, Structure, Chlorine Rotation, and Application in α‐Olefination of Nitriles by Primary Alcohols

“…further validates the coordination of ligands with palladium precursor (Figure 1). [15] Additionally, the HRMS data of C1 showed a peak at m/z 891.2028 which was correlated to [M + H] + ion (Figure s5 in SI).…”

Pd(ii) complexes bearing NNS pincer ligands: unveiling potent cytotoxicity against breast and pancreatic cancer

“…reported a palladium complex with a selenium analogue ligand where Pd–Se Ph (2.3651 Å) bond length is larger than that of Pd–S Ph bond lengths found in complexes C1 , C3 , and C4 due to the larger size of selenium. 36…”

Recent Progress on the Synthesis of Bipyridine Derivatives

“…Expanding on this approach, Singh et al developed dinuclear palladium pincer complexes incorporating a Pd-Pd bond based on N,N,Se-ligands [44]. Bipyridine compounds can be synthesized in good yield by combining the decarboxylation of picolinic acid and the C-H activation of pyridine using this complex as a catalyst (Figure 4b).…”