C−X (X = N, O) Cross-Coupling Reactions Catalyzed by Copper-Pincer Bis(N-Heterocyclic Carbene) Complexes

Abstract

Over the last two decades, N-heterocyclic carbene (NHC)–copper catalysts have received considerable attention in organic synthesis. Despite the popularity of copper complexes containing monodentate NHC ligands and recent development of poly(NHC) platforms, their application in C–C and C–heteroatom cross-coupling reactions has been limited. Recently, we reported an air-assisted Sonogashira-type cross-coupling catalyzed by well-defined cationic copper-pincer bis(NHC) complexes. Herein, we report the application of these complexes in Ullmann-type C–X (X = N, O) coupling of azoles and phenols with aryl halides in a relatively short reaction time. In contrast to other well-defined copper(I) catalysts that require an inert atmosphere for an efficient C–X coupling, the employed Cu(I)-pincer bis(NHC) complexes provide good to excellent yields in air. The air-assisted reactivity, unlike that in the Sonogashira reaction, is also affected by the base employed and the reaction time. With Cs2CO3 and K2CO3, the oxygen-generated catalyst is more reactive than the catalyst formed under argon in a short reaction time (12 h). However, the difference in reactivity is compromised after a 24 h reaction with K2CO3. The efficient pincer Cu-NHC/O2/Cs2CO3 system provides great to excellent cross-coupling yields for electronically diverse aryl iodides and imidazole derivatives. The catalyst scope is controlled by a balance between nucleophilicity, coordinating ability, and the steric hindrance of aryl halides and N-/O-nucleophiles.

Highly modulated supported triazolium-based ionic liquids: direct control of the electronic environment on Cu nanoparticles

“…54 (ii) Reduced yields were achieved for different halogen sources, because of the low reactivity Nanoscale Advances Paper observed for deactivated aryl halides on nucleophilic substitutions (C-X: I > Br > Cl). 57 In this regard, the molecular electrostatic potential (MEP) was calculated for Cu@SILP1-3. The MEP results show that charge polarisation takes place on Cu NPs aer the charge transfer between SILPs and Cu NPs (Fig.…”

Synthesis, characterization, and photoluminescent studies of three-coordinate Cu(i)–NHC complexes bearing unsymmetrically-substituted dipyridylamine ligands

“…Both [Cu(IPr)Cl] and [Cu(SIPr)Cl] precursors were prepared according to a slightly modied Cazin-Nolan procedure using CuCl, the imidazolium/imidazolinium salt, and K 2 CO 3 as a base. 37 Dipyridylamine ligands were obtained using a Buchwald-Hartwig coupling reaction between 2-bromopyridine and 2-aminopyridine derivatives. The optimal amount of Pd 2 (dba) 3 catalyst for these syntheses was found to be 1.0 mol%, half of the amount used previously for the symmetrical Me 2 -Hdpa ligands.…”

Synthesis, Aggregation Behavior, and Catalytic Activity in the Ullmann Reaction of Amphiphilic p-tert-Butylthiacalix[4]arene with Azidoalkylimidazolium Moieties

“…Медь-катализируемая реакция Ульмана, несомненно, является мощным инструментом для образования связи C-N и С-О. [14] Учитывая, что комплексные соединения меди с NHC лигандами, [15] в т.ч. полученные in situ из соли имидазолия и CuI, [16] проявляют высокую каталитическую активность в реакции Ульмана, нами была исследована каталитическая активность системы CuI+2 в реакции сочетания п-бромацетофенона с имидазолом а также некоторыми фенолами (Таблица 2).…”

“…Согласно полученным данным, при проведении реакции п-бромацетофенона с имидазолом с использованием только CuI конверсия составила всего 58 %, при добавлении же макроцикла 2 к CuI конверсия существенно увеличилась до 82 %, что превосходит активность известных в литературе каталитических систем, испытанных в схожих условиях. [15] Не менее эффективной оказалась комбинация CuI+2 и в реакции О-арилирования, которую проводили при более низкой температуре, принимая во внимание большую нуклеофильность (и, как следствие, реакционную способность) фенолятов по сравнению с азот-содержащими нуклеофилами. Так же, как и в случае N-арилирования, система CuI+2 оказалась эффективнее индивидуальной CuI.…”