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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:
Figure 1. Mechanism for a generic cross-coupling reaction with A) homogenous Pd in the presence of a ligand and B) heterogeneous, ligandless Pd as the Pd source. The role of the solid phase in heterogeneous metal catalyzed cross-coupling, then, is more subtle than one might expect.
In one important reaction type, a main group organometallic compound of the type R-M (where R = organic group, M = main group centre metal atom) reacts with an organic halide of the type R'-X with formation of a new carbon-carbon bond in the product R-R'. The most common type of coupling reaction is the cross coupling reaction. [1] [2] [3]
The first example of organogermanes used in transition-metal-catalyzed cross-coupling reaction was reported in 2004. [1] However, due to the toxicity, low reactivity (compared with other Ar–[M] nucleophiles) and poor stability of ArGeCl 3, this reaction was demonstrated not to be synthetically applicable.
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.
In organic chemistry, phosphonium coupling is a cross-coupling reaction for organic synthesis. It is a mild, efficient, chemoselective and versatile methodology for the formation of C–C, C–N, C–O, and C–S bond of unactivated and unprotected tautomerizable heterocycles. The method was originally reported in 2004. [1]
The most useful cross-coupling catalysts tend to be ones that contain palladium. Cross-coupling reactions have the general form of R′–X + M–R → R′–R + M–X and are used to form C–C bonds. R and R′ can be any carbon fragment. The identity of the metal, M, depends on which cross-coupling reaction is being used. Stille reactions ...
The reaction was described in 1963 by chemists Castro and Stephens. [ 1 ] [ 2 ] The reaction is similar to the much older Rosenmund–von Braun synthesis (1914) [ 3 ] [ 4 ] between aryl halides and copper(I) cyanide and was itself modified in 1975 as the Sonogashira coupling by adding a palladium catalyst and preparing the organocopper compound ...