Palladium-Catalyzed Tetrakis(dimethylamino)ethylene-Promoted Reductive Coupling of Aryl Halides

Abstract

Tetrakis(dimethylamino)ethylene (TDAE)/cat. PdCl(2)(PhCN)(2)-promoted reductive coupling of aryl bromides having either electron-donating or electron-withdrawing groups on their para- and/or meta-position proceeded smoothly to afford the corresponding biaryls in good to excellent yields. Notably, TDAE is such a mild reductant that easily reducible groups, such as carbonyl and nitro groups, are tolerate. A similar reductive coupling of ortho-substituted aryl bromides did not occur at all. The proper choice of palladium catalysts is essential for the reductive coupling; thus, PdCl(2)(PhCN)(2), PdCl(2)(MeCN)(2), Pd(hfacac)(2), Pd(2)(dba)(3), PdCl(2), and Pd(OAc)(2) were used successively for this reaction, but phosphine-ligated palladium catalysts such as Pd(PPh(3))(4), PdCl(2)(PPh(3))(2), and Pd(dppp) did not promote the reaction. The reductive coupling did not occur with nickel catalysts such as NiBr(2), NiCl(2)(bpy), and Ni(acac)(2). The TDAE/cat. palladium-promoted reductive coupling of aryl halides having electron-withdrawing groups took place more efficiently than that of aryl halides substituted with electron-donating groups. A plausible mechanism of TDAE/cat. palladium-promoted reaction is discussed.

Electro-reductive Homo-Coupling Reaction of Aryl Bromides in PdCl2(PPh3)2/Pyridinium Salt Double Mediatory Systems

“…Reductants so far studied include metal reductants such as Na, Li, and Zn, metal hydride reductants such as LiAlH 4 and NaBH 4 , inorganic reductants such as Na 2 S 2 O 3 , and organic reductants such as NADH, 1 ascorbic acid, 2 anion radicals of polycyclic aromatic compounds, 3 and tetrakis(dimethylamino)ethylene. 4 Among them, organic reductants are usually soluble in organic solvents, and, as the results, electron transfer to the substrates proceeds smoothly. Design and modification of the organic reductants are easily performed to suppress undesired side reactions.…”

An Economical, Green Pathway to Biaryls: Palladium Nanoparticles Catalyzed Ullmann Reaction in Ionic Liquid/ Supercritical Carbon Dioxide System

“…[14c-f] In these processes, reducing agents such as aldehyde, [14e] hydrogen gas, [17] formate salts, [18] alcohol, [19] glucose, [20] carbon monoxide, [21] ascorbic acid, [22] amine, [23] zinc [14f] and indium or germanium [10a] etc. were required for closing the reductive coupling cycle.…”

Facile and Efficient Reductive Homocoupling of Benzyl and Aryl Halides Catalyzed by Ionic Liquid [C12mim][CuCl2] in the Presence of Metallic Zinc and Copper

“…The usual synthetic methods for such a conversion include the Ullmann coupling [4][5][6], Suzuki coupling [7][8][9][10][11][12], Scholl reaction [13,14], Gomberg-Bachmann reaction [15,16], Stille reaction [17][18][19][20], and other couplings [21][22][23][24]. However, these above-mentioned protocols, in general, are invariably associated with one or more disadvantages, such as low yields, long reaction times, high reaction temperatures, high catalyst loading, tedious workup procedures, costly metal catalysts, difficulty of catalyst recovery, and environmental toxicity.…”