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In organic chemistry, a cross-coupling reaction is a reaction where two different fragments are joined. Cross-couplings are a subset of the more general coupling reactions. Often cross-coupling reactions require metal catalysts. One important reaction type is this:
The most common type of coupling reaction is the cross coupling reaction. [1] [2] [3] Richard F. Heck, Ei-ichi Negishi, and Akira Suzuki were awarded the 2010 Nobel Prize in Chemistry for developing palladium-catalyzed cross coupling reactions. [4] [5] Broadly speaking, two types of coupling reactions are recognized:
The Negishi coupling is a widely employed transition metal catalyzed cross-coupling reaction. The reaction couples organic halides or triflates with organozinc compounds, forming carbon-carbon bonds (C-C) in the process. A palladium (0) species is generally utilized as the catalyst, though nickel is sometimes used.
The mechanism of the Stille reaction has been extensively studied. [11] [23] The catalytic cycle involves an oxidative addition of a halide or pseudohalide (2) to a palladium catalyst (1), transmetalation of 3 with an organotin reagent (4), and reductive elimination of 5 to yield the coupled product (7) and the regenerated palladium catalyst (1).
The coupling of 2-chlorobenzoic acid and aniline is illustrative: [4] C 6 H 5 NH 2 + ClC 6 H 4 CO 2 H + KOH → C 6 H 5 N(H)−C 6 H 4 CO 2 H + KCl + H 2 O. A typical catalyst is formed from copper(I) iodide and phenanthroline. The reaction is an alternative to the Buchwald–Hartwig amination reaction.
The cross-coupling is carried out at room temperature with a base, typically an amine, such as diethylamine, [6] that also acts as the solvent. The reaction medium must be basic to neutralize the hydrogen halide produced as the byproduct of this coupling reaction, so alkylamine compounds such as triethylamine and diethylamine are sometimes used ...
This is a list of unsolved problems in chemistry. Problems in chemistry are considered unsolved when an expert in the field considers it unsolved or when several experts in the field disagree about a solution to a problem.
A typical example of classic Ullmann biaryl coupling is the conversion of ortho-chloronitrobenzene into 2,2'-dinitrobiphenyl with a copper - bronze alloy. [9] [10] 2 C 6 H 4 (NO 2)Cl + 2 Cu → (C 6 H 4 (NO 2)) 2 + 2 CuCl. The reaction has been applied to fairly elaborate substrates. Ullmann reaction