A Defined N-Heterocyclic Carbene Complex for the Palladium-Catalyzed Suzuki Cross-Coupling of Aryl Chlorides at Ambient Temperatures

Abstract

Highly active but sterically demanding: Ambient‐temperature Suzuki cross‐coupling of aryl chlorides is possible with a palladium(0) complex bearing two bulky, N‐heterocyclic carbene ligands (see structure). Nearly quantitative yields are obtained within two hours with some reagents, which makes this compound the most active catalyst known to date under these conditions.

Sterically induced differences in N-heterocyclic carbene transition metal complexes

“…In the structurally determined homoleptic bis-carbene complexes of the zero valent metals nickel, palladium and platinum, only structure type B is found [35][36][37][38][39][40][41][42][43]. The carbene ligands in these complexes have sterically demanding substituents at the nitrogen atom (mesityl, tert-butyl, adamantyl) [38][39][40][41][42][43], which raises the suspicion that the tilting of the carbene ligands may have steric reasons. The only described homoleptic complex with methyl substituted carbene ligand [Ni(IMe) 2 ] 1 2 was not structurally determined.…”

“…The neutral representatives [M(NHC) 2 ] (M = Ni, Pd, Pt) (see Fig. 3) [36][37][38][39][40][41][42][43] without exception realise structure type B as far as they are structurally characterised. This is obviously due to the sterically demanding substituents.…”

“…The steric influence of the wingtip substituents on the structure of a transition metal carbene complex is most readily seen in the non-parallel coordination of the carbene ligands in the homoleptic [M(NHC) 2 ] complexes (M = Ni, Pd, Pt) [35][36][37][38][39][40][41][42][43] (see Fig. 3).…”

Activity and Recyclability Improvement Through Adjusting the Tethering Strategy for Pd-Catalyzed Suzuki–Miyaura Coupling Reaction of Aryl Chlorides

“…They chose triethylamine (TEA) as a ''throw-away'' ligand to synthesize NHCPd complex, (IPr)PdCl 2 (TEA) (IPr = N,N 0 -bis(2,6-diisopropylphenyl)imidazol-2-ylidene), which was highly efficient for Suzuki coupling reactions. Although these catalysts performed excellent catalytic activity [19][20][21][22], they have some limitations in terms of separation, recycling and contamination of ligand residues to products [23]. In the past few years, heterogeneous catalysts such as Pd/C [24], Pd/SiO 2 [25,26], Pd/KF-Al 2 O 3 [27], Pd/SWNT [28] and Chitosanbased Pd catalysts [29], were developed to overcome these limitations.…”

Sulfur-Ligand/Pd-Catalyzed Cross-Coupling Reactions of Aryl Halides with Arylboronic Acids Under Aerobic Conditions

“…However, many phosphines are sensitive to air and moisture resulting in limitations on their applications [12]. Therefore, the application of alternative ligands in metal-catalyzed synthetic transformations opens up new opportunities in catalysis [13][14][15][16][17][18]. Sulfur-containing compounds were traditionally categorized as catalyst poisons due to their strong coordinative and adsorptive properties, which rendered them totally ineffective as catalysts [19,20].…”