Aryl halides reactions with metal cations

Unsymmetrical as well as symmetrical anhydrides are often prepared by the treatment of an acyl halide with a carboxylic acid salt. The compound C0CI2 has been used as a catalyst. If a metallic salt is used, Na , K , or Ag are the most common cations, but more often pyridine or another tertiary amine is added to the free acid and the salt thus formed is treated with the acyl halide. Mixed formic anhydrides are prepared from sodium formate and an aryl halide, by use of a solid-phase copolymer of pyridine-l-oxide. Symmetrical anhydrides can be prepared by reaction of the acyl halide with aqueous NaOH or NaHCOa under phase-transfer conditions, or with sodium bicarbonate with ultrasound. 

Nwokogu, G.C., Wong, J.-W., Greenwood, T.D. and Wolfe, J.F. (2000) Photostimulated reactions of phenylacetic add dianions with aryl halides. Influence of the metallic cation on the regiochemistry of arylation. Organic Letters, 2, 2643—2646. 

C.iii.c. Preparation of Small Molecules for Materials Science. Pd-catalyzed amination has also been used to prepare small molecules that are useful as hole-transport materials, selective metal-cation detection systems, and dyestuffs. As mentioned briefly in the section on reacting diarylamines with aryl halides, Marder and co-workers used palladium chemistry to form triarylamines, which are useful as hole-transport layers. Reactions of primary arylamines with aryl halides using DPPF-hgated palladium as catalyst allows for the selective addition of one aryl halide, followed by the addition of a second aryl halide to form mixed triarylamines, as shown in Eq. 42. This procedure has been used to generate unsymmetrical triarylamines that are analogs of TPD, as shown in Eq. 43. hi addition, they have used aminoferrocene as a substrate to conduct diarylations to form N, A-diarylaminoferrocenes. ... 

These photochemical reactions with olefins can be considered a cationic analogue of the Meerwein arylation that occurs with nucleophilic rather than with electrophilic alkenes. The rapid cleavage of excited aryl halides and esters in polar solvent and the efficient trapping of the formed aryl cation render these arylations normally less-sensitive towards dissolved oxygen, in contrast to many other photochemical reactions. These characteristics, along with the mild reaction conditions and the simple experimental set-up, make the photochemical method a complementary and valuable alternative to metal-mediated or -catalyzed reactions. 

The path for the formation of the Grignard reagent is believed to involve transfer of an electron from the sea of electrons present in the metal into the lowest unoccupied molecular orbital (LUMO) of the alkyl (aryl) halide. The radical anion/ surface-metal cation can continue with the transfer of a second electron or, depending on steric and electronic circumstances, an alkyl (aryl radical) and halogen anion can be produced. Coupling and elimination products occasionally accompany reduction and those products can be rationalized as being derived from free radicals. The halide anion remains associated with the surface as it does with most reactions in solvents that cannot support ionic materials. The alkyl radical would be free from that constraint. 

The aryl ether linkage is important in many natural products and pharmaceuticals, including the antibiotic vancomycin [196]. Diaryl ethers have been efficiently prepared by the coupling of fluo-robenzonitriles with a series of phenols in DMSO using potassium carbonate as a base catalyst and with microwave irradiation [197]. A DPT study of the reaction of alkali metal phenoxides with fluo-robenzenes indicated that the role of the metal cation is to aid the binding of the aryl halide and to facilitate fluoride displacement [198]. 

---