Cobalt‐Catalyzed Formation of Symmetrical Biaryls and Its Mechanism

Abstract

Effective devotion: An efficient cobalt-catalyzed method devoted to the formation of symmetrical biaryls is described avoiding the preparation of organometallic reagents. Various aromatic halides functionalized by a variety of reactive group reagents are employed. Preliminary DFT calculations have shown that the involvement of a Co(I)/Co(III) couple is realistic at least in the case of 1,3-diazadienes as ligands (FG = functional group).

Graphene-oxide-supported CuAl and CoAl layered double hydroxides as enhanced catalysts for carbon-carbon coupling via Ullmann reaction

“…As mentioned in the introduction, there are less than 7 examples that show good yield (up to 65%) on homocoupling reactions using Co catalysts and those works were developed back in 1964. Recently, yields of up to 84% have been reported [52] for the same reaction using CoBr2 but the substitution of phenyl groups by an electron withdrawing group was required resulting in the corresponding substituted biphenyl. When using halobenzenes the only reported yield falls down to 32% (entry 8 in Table 2) and only shows better performance when using Grignard reagents (entry 9 in Table 2).…”

“…Cobalt has been extensively used for cross coupling reactions but only a handful of homocoupling reactions with good selectivity have been reported and all of them using substituted benzylic Grignard reagents [49]. It was not until 45 years later when Gosmini described good yields in the formation of unsymmetrical biaryls first [50,51] and symmetrical biaryls later [52] both catalysed by cobalt in combination with manganese dust as reducing agent. When substituting phenyl groups by an electron withdrawing group yields of up to 84% have been reported.…”

Cobalt‐Catalyzed C−C Homocoupling

“…[10] For a few years, our group has already reported efficient Co-catalyzed reductive cross-couplings, such as aryl-aryl, aryl-alkyl, allyl-alkyl cross couplings, [11] and homocoupling of aryl halides. [12] Therefore, we investigated an alternative C sp 3 À C sp 3 homocoupling reaction using a simple cobalt catalyst with the objective to develop a more [b] 9 addition of 40 mol% allyl chloride before TFA 30…”

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

“…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. Reductive coupling reactions using transition metal complexes as catalysts are another important methods for the formation of carbon-carbon bonds, and a variety of reagents, such as palladium [25][26][27][28][29], nickel [30][31][32], iron [33,34], vanadium [35,36], lanthanum [37], zinc [38,39], and other complexes [40][41][42][43][44], have been developed for this conversion. However, most of the procedures still suffered from the use of expensive reagents, difficulties in work up, environmental hazards, and difficulties in recycling of the catalyst.…”