1.2- dihaloarenes

The reaction has been applied to the synthesis of cyclophane-type structures by use of dihaloarenes and Grignard reagents from a, w-dihalides. 

It is suggested46 that the reaction mechanism involves initial electron transfer from Ph3.Sn to the arene on irradiation to form the Pl Sn- radical and Ar. Disubstitution is also observed on irradiation of dihaloarenes, with a mechanism as outlined in Scheme 9. 

In a slightly less convenient procedure, but one which has general versatility, carbonylation of aryl (or vinyl) palladium compounds produces aryl, heteroaryl, and vinyl carboxylic acids. As with the other procedures, immediate upon its formation, the carboxylate anion migrates to the aqueous phase. Consequently, haloaromatic acids can be obtained from dihaloarenes, without further reaction of the second halogen atom, e.g. 1,4-dibromobenzene has been carbonylated (90% conversion) to yield 4-bromobenzoic acid with a selectivity for the monocarbonylation product of 95%. Additionally, the process is economically attractive, as the organic phase containing the catalyst can be cycled with virtually no loss of activity and ca. 4000 moles of acid can be produced for each mole of the palladium complex used [4],... 

Heck in one of his first papers already demonstrated the feasibility of applying the palladium-catalyzed crosscoupling of aryl and alkenyl halides with alkenes repetitively on appropriate oligofunctional substrates. For example, twofold coupling of 1,4-diiodobenzene with styrene furnished 1,4-distyrylbenzene in 67% yield (Scheme 1). Since then, a large number of ortho-, meta-, and / r< -dihaloarenes and -heteroarenes have been subjected to twofold Heck reactions with various alkenes (Schemes 2-4). 

The cross-coupling polymerization with dihaloarenes leads to poly(phenylene-vinylene)s (PPVs), which are widely employed as conductive and electroluminescent polymers. ... 

Heitz has performed the cross-coupling polymerization using two-step one-pot process. The first step is the reaction of 1,4-diiodobenzene 107 with 2 equiv. of 2-methyl-3-butyn-2-ol 108 at room temperature in the presence of an aqueous base to give the protected bisalkyne 109. Following polycondensation with another equivalent of dihaloarene 110 leads to the corresponding polymer 111 at 100°C (Equation (53)). The overall yield of 111 was 50-90% and the average molecular weight (M ) was 1400-48 200. 

TABLE 9. Halogen-magnesium exchange of dihaloarenes followed by reaction with propanal... 

Digermanes, unsymmetrically substituted, 3, 787 Digermenes, preparation, 3, 796 Digestion studies, stability, 12, 612-613 DIGISIM, in cyclic voltammetry, 1, 282-283 Digital simulations, in cyclic voltammetry, 1, 282 Dihalides, in chromium mononitrosyl complexes, 5, 302 Dihaloarenes, cross-coupling polymerization, 11, 659... 

Haloarene derivatives used for coordination polycondensation are primarily represented by halostyrenes and haloarylacetylenes which undergo selfcoupling to poly(arylene vinylene)s [scheme (2)] and poly(aryleneacetylene)s [scheme (3)] respectively, and by dihaloarenes which, mainly in a combination with alkenes or divinylarenes and acetylenes or diacetylenes, undergo crosscoupling to poly(arylene vinylene)s [schemes (4) and (5)] and poly(arylene acetylene)s [schemes (6) and (7)] respectively [2] ... 

The transition metal-catalysed cross-coupling of arene diboronic acids with dihaloarenes also yields poly(arylene)s [2] ... 

It is worth noting that arene boronic acids and arene diboronic acids are synthesised from the corresponding halo- and dihaloarenes. 

Poly(arylene)s are also formed in analogous coordination heteropolycondensation of dihaloarenes with di(alkylmetal)arenes, especially di(tributyltin)ar-enes [2] ... 

Also, the coordination polycondensation of dihaloarenes via reductive coupling with metals or metal complexes, catalysed by transition metal complexes, leads to polyarylenes [2,3] ... 

In addition to aryl alkynyl coupling reactions involving dihaloarenes and acetylenes or dialkynylarenes which lead to poly(arylene acetylene)s, it is worth noting that these polymers have also been obtained by the Pd(0)-catalysed heteropolycondensation of dialkoxy-substituted dibromoarenes with bis(tribu-tylstannyl)acetylenes [122]. 

The dehalogenating polycondensation of dihaloarenes to poly(arylene)s, involving reductive coupling with metals such as magnesium or zinc [scheme... 

In connection with nickel-catalysed reductive coupling reactions of dihaloarenes, leading to poly(arylene)s, the copper-catalysed reductive carbenoid coupling reactions involving substituted bis(dichloromethyl)arenes and metals or other reductants should be mentioned. The reductive carbenoid coupling of bis(phenyldichloromethyl)arene with zinc in the presence of Cu-based catalysts is shown below ... 

Coordination carbonylation polycondensation has been extended from the synthesis of polyamides [scheme (15)] and polyarylates [scheme (16)] to reactions using other nucleophilic monomers that, with dihaloarenes and carbon monoxide, yield poly(imide-amide)s, poly(acylhydrazide)s, and poly(benzoxa-zole)s [165,170,171],... 

Explain why carbon-heteroatom carbonylative coupling reactions are preferably carried out with palladium-based catalysts give an example of the catalytic cycle in the carbonylative polycondensation of dihaloarene and bisphenol, leading to a polyester. 

New nickel-benzyne complexes (143-147) have been prepared by reaction of o-dihaloarenes with Ni(COD)2 in the presence of a trialkylphosphine followed by reduction of the oxidative addition product with either Li or 1% Na/Hg in ether [e.g., Eq. (23)]. The oxidative addition reaction depends on the nature of substituents on the arene and fails to occur when strong electron-donating groups are present. Based on NMR and mass spectrometry (MS) data, the new complexes were formulated as monomeric. It had been... 

Oxygen functionalities may readily be introduced into aromatic rings by nucleophilic displacement of an aryl halide by an alkoxide226-236. The reaction may be performed under phase-transfer conditions using phenoxide as the nucleophilic anion237- 39. In the case of dihaloarene substrates, selective mono displacement is possible240,241. 

Stepwise double coupling of two different arylboronic acids with a dihaloarene afforded one-pot, two-step method for synthesizing unsymmetrical teraryls, quateraryls, and other higher order polyaryls.882 The first total synthesis of dragmacidin D involved a sequential double coupling of two different pinacol 3-indoleboronic esters (ArBpin Equation (207)).882... 

Tellurium and the following 1,2-dihaloarenes did not yield any telluranthrenes under the conditions used for the synthesis of telluranthrene1 ... 

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