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

Abstract

Dinuclear gold(I)-N-heterocyclic carbene complexes were developed for the hydrohydrazidation of terminal alkynes. The gold(I)-N-heterocyclic carbene complexes 2a-2b were synthesized in good yields from silver complexes synthesized in situ, which in turn were obtained from the corresponding imidazolium salts with Ag 2 O in dichloromethane as a solvent. The new airstable gold(I)-NHC complexes, 2a-2b, were characterized using NMR spectroscopy, elemental analysis, infrared, and mass spectroscopy studies. The gold(I) complex 2a was characterized using X-ray crystallography. Bis-N-heterocyclic carbene-based gold(I) complexes 2a-2b exhibited excellent catalytic activities for hydrohydrazidation of terminal alkynes yielding acylhydrazone derivatives. The working catalytic system can be used in gram-scale synthesis. In addition, the catalytic reaction mechanism of the hydrohydrazidation of terminal alkynes by gold(I)-NHC complex was studied in detail using density functional theory.

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] …”

“…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.…”

Metal‐Free K2S2O8‐Mediated Direct Hydrazonation of Methylene in Pyrazoline‐5‐ones

“…[11] In 2020, Yadav et al synthesized acyl hydrazone compounds with acyl hydrazides by catalytic activation of terminal alkynes in the presence of an Au(I)-N-heterocyclic carbene complex (Scheme 1c). [12] Unfortunately, to achieve direct activation of pyrazoline-5-one methylene, the aforementioned protocols are unsuitable or suffer from drawbacks such as multistep processes, metal catalysis, harsh reaction conditions, and potentially hazardous reactants.…”