Cross aryl fluorides

Aryl crown ethers, in hexaruthenium carbido clusters, 6, 1008 Aryl cyanides, with Ni(0) complexes, 8, 47 Aryldiazoalkanes, with bis-Gp Ti, 4, 580-581 a-Arylenamides, asymmetric hydrogenation, 10, 28 Arylenes, with platinum(II), 8, 491 Aryl ethers, via cross-coupling with copper, 10, 650 with palladium, 10, 654 Aryl fluorides... 

A further advantage is the possible in situ generation of catalysts from simple metal salts or complexes (e. g., Ni(OR)2, PdCU) and azolium salts. The nickel-catalyzed Grignard cross-coupling of aryl chlorides at room temperature [123] and the activation of aryl fluorides [136] are convincing examples. 

The first examples of Rh-catalyzed C-S bond formation were reported by Yamaguchi in 2008 [128]. The process involves the coupling of disulfides with aryl fluorides, which remain atypical electrophiles for cross-coupling. These conditions afford excellent selectivity for C-F bond cleavage over other C-X bonds (13) (dppBz =... 

Equation 13 Rhodium catalyzed disulfide, aryl fluoride cross coupling [128]... 

Nickel also catalyses the cross-coupling of aryl fluorides with organozinc reagents. To perform partial C-F bond activation of poly-fluoroaromatics, the existence of a directing group is often necessary (Scheme 14.6). However, the combination of Ni(acac)2 and POP can... 

Scheme 2.13 The Suzuki-Miyaura cross-coupling of aryl fluorides under conditions developed by the Chatani group.

Scheme 2.14 Mechanistic rational for the Suzuki-Miyaura cross-couplings of aryl fluorides.

Air-stable sterically congested phosphine oxides such as 48 are also excellent Ug-ands for the nickel-catalyzed cross-coupling of aryl fluorides [43] (Scheme 5.8). The association of nickel salts with these so-caUed heteroatom-substituted secondary phosphine oxide (HASPO) ligands leads to species reactive enough to activate the generally inert arene-fluorine bond (BDE Ph-F = 126kcalmol ). This improved reactivity has been explained by the formation of a bimetallic species 52 (Scheme 5.8), which facilitates the oxidative insertion step that proceeds via transition state TSl (Figure 5.1) [44]. 

Scheme 5.8 Ni-catalyzed cross-coupling reaction of arylmagnesium reagents with aryl fluorides in the presence of HASPO ligands [43],...

A highly innovative approach exploited the photolysis of various p-functionaHzed anisole precursors 55 in the presence of terminal alkynes such as 56, EtjN, and trifluoroethanol (TFE). The initially formed p-functionaUzed methoxyphenyl cations reacted with the terminal alkynes to provide the cross-coupled products 57 in yields between 60 and 90% (Scheme 9.19) [161]. This contains also the first reported alkynylation of aryl fluorides, mesylates, and phosphates. 

Rieke calcium is exceptionally highly reactive. Thus, fluorinated, chlorinated, brominated, and chloromethylated cross-linked polystyrene resins are all successfully converted to the corresponding calcium reagents. It should be noted that few metals undei o oxidative addition to aryl fluorides. Thus, it is noteworthy that Ca reacts with / -fluoropolystyrene at room temperature to... 

A year later, Hermann and co-workers showed that these Corriu-Kumada cross-coupling were efficiently obtained under NHC-Ni catalysis with aryl fluorides as starting materials. They showed that an in situ generated species worked similarly if not better than a pre-formed [(NHC)2Ni] complex. This observation suggested that the catalytic active species would be a zero-valent nickel coordinated with only one N-heterocyclic carbene ligand. The formation of a 12-electrons complex would be evidently favored in an in situ process. Both catalysts were active with electron-rich or electron-poor fluoroarenes as well as with congested organometallic species (Equation (10.12)). 

Can aryl triflates be converted into aryl fluorides through metal-catalyzed cross-coupling chemistry ... 

Trifluoromethylalion of aryl iodides was carried out by the fluoride ion in duced cross-coupling reaction of aromatic iodides with tnfluoromethyltnalkyl-silanes in the presence ofcopper(I) salts [219 (equation 147) Some pentafluoro- ethyl derivative was also formed This methodology was extended to pentafluoroethyl-and heptafluoropropyltriethylsilanes [2/9]... 

The palladium-catalyzed cross-coupling of alkenylsilanols has been extensively studied with respect to the structure of both the silicon component and the acceptor halide. The preferred catalyst for coupling of aryl iodides is Pd(dba)2 and for aryl bromides it is [allylPdCl]2. The most effective promoter is tetrabutylammonium fluoride used as a 1.0M solution in THF. In general the coupling reactions occur under mild conditions (room temperature, in 10 min to 12 hr) and some are even exothermic. 

Kotschy et al. also reported a palladium/charcoal-catalyzed Sono-gashira reaction in aqueous media. In the presence of Pd/C, Cul, PPI13, and z -Pr2NH base, terminal alkynes smoothly reacted with aryl bromides or chlorides, such as 2-pyridyl chloride, 4-methylphenyl bromide, and so on, to give the expected alkyne products in dimethyl-acetamide (DMA)-H20 solvent. Wang et al. reported an efficient cross-coupling of terminal alkynes with aromatic iodides or bromides in the presence of palladium/charcoal, potassium fluoride, cuprous iodide, and triph-enylphosphine in aqueous media (THF/H20, v/v, 3/1) at 60°C.35 The palladium powder is easily recovered and is effective for six consecutive runs with no significant loss of catalytic activity. 

Fluoride-activated monoorganotin derivatives can be used in cross-coupling with aryl or vinyl iodides to transfer a very wide range of organic residues, including alkyls which are not normally reactive (Equation (12)) 62... 

The application of bases other than fluoride for activation of organosilicon compounds to crosscoupling is documented. NaOH can replace fluoride in the cross-coupling of aryl and alkenyldichloroalkylsilanes with aryl halides, including chlorides. Apart from providing milder reaction conditions, the reaction in the presence of NaOH is applicable to a wider range of substrates ((85) and (86)).294... 

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