Research In Ni（acac）₂/N-Heterocyclic Carbene Catalyzed Heck Reaction And N-Arylation Of Heterocycles In Pure Water

Since isolated by Arduengo in1991, N-heterocyclic carbene (NHCs) have been applied in several chemistry areas. However, since NHCs are air and moisture sensitive, they are usually released from NHCs precursor under specific condition. Some prominent member of NHCs precursors are the sterically encumbered imidazolium salts IPr·HCl (1,3-bis-{2,6-diisopropylphenyl} imidazolium chloride) and IMes·HCl (1,3-bis-{2,4,6-trimethylphenyl}imidazolium chloride), which can also be considered as analogues of bulky and electron-rich phosphanes.In this paper, we use trimethylchlorosilane instead of concentrated HCl to react with1,4-diaryl-1,4-diazadienes, paraformaldehyde to generate N-heterocyclic carbene precursor IPr·HCl and IMes·HCl. Compared with the previous reports, the reaction time is shortened with the huge yield increase (85%and81%). Then we first discovery the combination of NHC precursors (IPr·HCl and IMes·HCl) with Ni(acac)2catalyst system, which was used in Heck reaction of acrylate with aryl iodide and aryl bromide. The products were characterized by NMR spectrometer.After that, we began a research about Ullmann type reaction in the aqueous phase. Activated-copper powder is an efficient catalyst for the N-arylation of heterocycles with aryl halides. We report a simple, practical, and green catalytic system for the arylation of N-heterocycles, which uses tetrabutylammonium bromide (TBAB) as the phase-transfer catalyst, LiOH as base and pure water as the solvent under ligand-free conditions, and give the corresponding products in good yields (23%-87%). This method avoids the use of toxic organic solvents and stringent inert conditions. Not only aryl-iodides and-bromides, but also some aryl-chlorides can be served as arylating reagents of N-heterocycles. And products were characterized by nuclear magnetic resonance spectrometer and GC-MS.