Sonogashira Couplings Catalyzed by Collaborative (N-Heterocyclic Carbene)-Copper and -Palladium Complexes

Abstract

A general protocol for the Sonogashira reaction using a 100:1 combination of (N-heterocyclic carbene)-Cu and (N-heterocyclic carbene)-Pd complexes is presented. Catalyst loadings of 1 mol % (NHC)-Cu and 0.01 mol % (NHC)-Pd allow for the coupling of aryl bromides and aryl alkynes, in air and in a non-anhydrous solvent, in high yields.

Copper–NHC complexes in catalysis

“…Ullman and Sonogashira couplings were carried out [120,121]. Recently, Navarro and co-workers reported a collaborative copper/palladium methodology [122]. In combination to Pd(SIPr)(Cl) 2 (TEA) complex, the activity of Cu(Cl)(NHC) complexes was evaluated for the coupling of 3-bromotoluene and phenylacetylene.…”

[(IPent)PdCl2(morpholine)]: A Readily Activated Precatalyst for Room‐Temperature, Additive‐Free Carbon–Sulfur Coupling

“…Next, we evaluated the substrate scope of the transformation employing precatalyst 11 d. We first studied the reaction of thiophenol (15) with a variety of aryl and heteroaryl halides (Table 3; [17][18][19][20][21][22][23][24]. The reactions performed well under the optimized conditions, with both sterically and/or electronically deactivated oxidative addition partners well tolerated with many reactions completing in just an hour or two.…”

“…We began our study with the preparation of a number of [(NHC)PdCl 2 (morpholine)] complexes (11 a-e; Scheme 2) [21] and evaluated their activity in aryl sulfination. Treating readily accessible [{(NHC)PdCl 2 } 2 ] dimers with a slight excess of morpholine in dichloromethane furnished analytically pure complexes after simple filtration through a plug of neutral alumina.…”

Unimolecular tetrakis-piperidine-4-ol: an efficient ligand for copper and amine free Sonogashira coupling

“…Considering cost factor and ease of handling, we choose Pd/C for further optimization. Inspection of various inorganic and organic base additives (entries 19-27) indicated K 2 CO 3 to be better (entry 5 vs. entries [19][20][21][22][23][24][25][26][27]. Varying the ligand concentration 0.5 mol% (entry 28) or Pd/C to 0.5 mol% (entry 29) resulted in lower yields of 5g.…”