DAB-Cy as an inexpensive and effective ligand for palladium-catalyzed homocoupling reaction of aryl halides

Versatile Synthesis of Pentalene Derivatives via the Pd-Catalyzed Homocoupling of Haloenynes

“…Such enynes are readily accessible via a variety of synthetic methods , and prove to be viable substrates in the pentalene coupling reaction (entry 6; Figure ). However, in this demanding coupling, the alkenyl iodide provided significantly higher yields (60%) relative to the alkenyl bromide (20%); again, this result is consistent with reports on Pd-catalyzed Ullmann couplings. , …”

“…Recent reports have described the Pd-catalyzed homocoupling of aryl halides with reducing agents such as zinc, 22 indium, 23 hydrogen gas, 24 formate salts, 25 hydroquinone, 26 alcohols, 27 and amines. 28 Screening of various reaction conditions with such reductants revealed that the highest yields of dibenzopentalene (>80%) were obtained in the presence of 2 equiv of hydroquinone and Cs 2 CO 3 (entry 1, Table 1).…”

Redox‐Active p‐Quinone‐Based Bis(pyrazol‐1‐yl)methane Ligands: Synthesis and Coordination Behaviour

“…[36] Recently, homocoupling reactions of aryl halides have been achieved with the help of Pd II catalysts that contain 1,4-diazabutadiene ligands in the presence of stoichiometric amounts of p-hydroquinone. [37] For a related reaction, a mechanistic model that provides an insight into the role of the p-hydroquinone reagent has been proposed. [38] Thus, for applications in catalysis and materials science, mono-(e.g., 2 a-2 c; Scheme 1) and ditopic (4; Scheme 1) phydroquinone-based bis(pyrazol-1-yl)methane ligands have been included in our investigations and their synthesis, reactivity and coordination behaviour will be described herein.…”

Homocoupling Reaction of Aryl Halides Catalyzed by Metal Cations in Isostructural Coordination Polymers

“…Historically, the Ullmann reaction of aromatic halides was the first successful method to prepare symmetric biaryls by copper metal as catalysts. As the Ullmann reactions demand the expenditure of equimolar mixtures of copper and a severe reaction temperature of over 200 °C, , multifarious catalysts, such as nickel, palladium, MnCl 2 , FeCl 3 , CoBr 2 , CuCl 2 , etc., were introduced into the reaction subsequently with milder reaction conditions. − In the homocoupling reaction catalyzed by palladium or nickel, a reducing agent, such as carbonic monoxide gas, hydroquinone (HQ), or hydrogen gas, is necessary. − However, the above reactions involve Grignard reagents, causing the reactions to be moisture-sensitive and difficult to control. The traditional catalysts are usually homogeneous catalysts, , which makes their cyclic utilization almost impossible.…”