Well‐Defined N‐Heterocyclic Carbene‐Palladium Complexes as Efficient Catalysts for Domino Sonogashira Coupling/Cyclization Reaction and C‐H bond Arylation of Benzothiazole

Abstract

Well‐defined and air‐stable PEPPSI (Pyridine Enhanced Precatalyst Preparation Stabilization and Initiation) themed palladium bis‐N‐heterocyclic carbene complexes have been developed for the domino Sonogashira coupling/cyclization reaction of 2‐iodophenol with a variety of terminal alkynes and C‐H bond arylation of benzothiazole with aryl iodides. The PEPPSI themed palladium complexes, 2a and 2b were synthesized in good yields from the reaction of corresponding imidazolium salts with PdCl2 and K2CO3 in pyridine. The new air‐stable palladium‐NHC complexes were characterized by NMR spectroscopy, X‐ray crystallography, elemental analysis, and mass spectroscopy studies. The PEPPSI themed palladium(II) bis‐N‐heterocyclic carbene complexes 2a and 2b exhibited excellent catalytic activities for domino Sonogashira coupling/cyclization reaction of 2‐iodophenol with terminal alkynes yielding benzofuran derivatives. In addition, the palladium complexes, 2a and 2b successfully catalyzed the direct C‐H bond arylation of benzothiazole with aryl iodides as coupling partners in presence of CuI as co‐catalyst.

Phosphine‐Free Bis(imino)pyridine‐Based Pincer Palladium(II) Complexes as Catalysts for C−H Bond Arylation of Azoles with Aryl Iodides

“…Punji and coworkersreported the C−H bond arylation of azoles using 0.5 mol% phosphine‐free (quinolinyl)amido‐based pincer palladium complexes [1b] . In 2019, our group also reported PEPPSI (Pyridine Enhanced Precatalyst Preperation Stabilization and Initiation) based bis ‐NHC palladium complexes catalyzed C−H bond arylation of benzothiazole using 1 mol% catalyst [12] …”

“…[1b] In 2019, our group also reported PEPPSI (Pyridine Enhanced Precatalyst Preperation Stabilization and Initiation) based bis-NHC palladium complexes catalyzed CÀ H bond arylation of benzothiazole using 1 mol% catalyst. [12] Experimental Section General procedures.All manipulations were carried out under an atmosphere of nitrogen or in air. Solvents were purchased from commercial sources.…”

“…In 2019, we have reported a series of palladium based PEPPSI complexes for C−H bond arylation of benzothiazoles with aryl iodides [12] . To the best our knowledge, the bis (imino)pyridine palladium(II) complexes for C−H bond arylation of benzothiazole with aryl halides is not reported yet.…”

“…[11] In 2019, we have reported a series of palladium based PEPPSI complexes for CÀ H bond arylation of benzothiazoles with aryl iodides. [12] To the best our knowledge, the bis(imino)pyridine palladium(II) complexes for CÀ H bond arylation of benzothiazole with aryl halides is not reported yet. During the course of investigation for designing the efficient phosphine-free transition metal based catalysts for CÀ H bond arylation of azoles, we found that the bis(imino)pyridine-based palladium(II) pincer complexes showed efficient catalytic activity in CÀ H bond arylation of benzothiazole with aryl iodide.…”

Dinuclear gold(I)‐N‐heterocyclic carbene complexes: Synthesis, characterization, and catalytic application for hydrohydrazidation of terminal alkynes

“…[4] As a part of our study on designing new transition metal-based catalysts for C-C and C-heteroatom bond-forming reactions, [5] we have reported a series of well-defined palladium catalysts supported by bis-N-heterocyclic carbene ligands for C-H bond arylation of benzothiazole and domino Sonogahsira coupling/cyclization reaction. [6] Based on an earlier work on catalytic performances of dinuclear complexes, analogs of gold(I) complexes of the bis-N-heterocyclic carbene ligands have been synthesized, and their catalytic activity in C-heteroatom bond-forming reactions has been studied.…”