Fluoroarene complexes

Arylpiperazines can be prepared in a one-pot procedure by ipso SNAr of piperazine derivatives with //6-fluoroarene complexes la, 33a,b,d. Indeed, piperazine derivatives react with fluorobenzene derivatives in DMSO in the presence of K2CO3 at 80 °C to give, after 2.5 h, complexes 3m and 3k (Nu = piperazine) in good yields (Scheme 18) [34]. Piperazine itself may be used as a nucleophile and gives the monoarylpiperazine derivative uncontaminated by any symmetrical N,N -bis(aryl)piperazine, allowing the direct preparation of unprotected compounds. 

The addition of two nucleophiles to a coordinated //6-arene is a synthetically important goal. A one-pot synthesis of 1,3-disubstituted cyclohexadienes involving an initial ipso addition to fluoroarene complexes is possible. Indeed, p-fluorotoluenetricarbonylchromium complex 22c reacts with isobutyronitrile carbanion (2 equiv.) in THF to give, after 5 days at —30 °C and acidic treatment under CO atmosphere, the cyclohexadiene 66 in 47 % yield (Scheme 31) [53] the yield can reach 75 % after several weeks Carbon monoxide was used in order to decoordinate the // -cyclohexadiene intermediate and to recover Cr(CO)6 needed for the preparation of the starting material [54]. 

There are only a few examples of displacement of a fluorine atom in a cross-coupling reaction. With tricarbonylchromium complexes of fluoroarenes as substrates, cross-coupling with both boronic acids and vinylstannanes has been realized. Interestingly, only PMe3 is effective as ligand in this reaction (89).2" See Section 9.6.3.4.10 for an example of the involvement of unactivated fluoroarenes in cross-coupling reactions. 

A comparison of the yields of para-substituted [18F]fluoroarenes indicate that (i) acetyl hypofluorite is an inferior fluorination agent for the fluorodegermylation reaction and (ii) the aromatic substituents have considerable influence over the reactivity of the fluorination. A decrease in the fluorodegermylation yield was observed with electron-withdrawing aromatic substituents. The electrophilic aromatic degermylation reaction is thought to proceed via a cr-complex intermediate (Scheme 3). It has been hypothesized that the yield of aryl fluoride is influenced to some extent by the aromatic substituents ability to stabilize the cr-complex intermediate. 

Substitution with amine nucleophiles in the series of chlorotoluene complexes showed that the substitution is direct no cine or tele substitution was observed.75 The analogous [(fluoroarene)FeCp]+ complexes are known, but less well developed. Kinetic studies show that the fluoro derivatives are more reactive compared to the chloro analogs.47... 

The reactivity of complexed haloarenes toward thiolates has been studied, and it has been reported that o-, m-, and p-dichlorobenzenetricarbonylchromium complexes 18a-c react with thiolates (RS R = Me, nBu, tBu Scheme 17, path i) under phase-transfer conditions or in DMSO to give 39 and 40a-c. The ortho- and para-complexes 18a and 18c undergo stepwise substitution of the two Cl atoms in a reaction sequence that can be easily controlled by the amount of added thiolate. The meta complex 18b shows a lower selectivity and gives a mixture of mono- and disubstituted products even in the presence of substoichiometric amounts of thiolate (Scheme 17) [22]. Similarly, LiCH(C02Et)CN and BuSH react with the o-dichlorobenzene complex 18a to give complex 39d and then disubstituted arene 40d, showing that this substitution can be performed with two different nucleophiles (Scheme 17) [23]. Phase-transfer catalysis has also been applied to fluoroarene-Cr(CO)3 complexes, which are more reactive toward thiolates than are the corresponding chloro derivatives [22]. 

Fluoroarene-Cr(CO)2L complexes 33p [L = CO, PPh3, P(OPh)3, P(pyrrolyl)3, P(pyrolyl)2 (NMeBn)], where L is a potential linker ligand for solid-phase synthesis, have been evaluated with regard to the rates of nucleophilic substitution by amines [35]. The preparative and kinetic results indicate that SNAr reactions on tris(pyrrolyl)phosphine-modified fluoroar-enechromium complexes proceed rapidly and with high efficiency, and are thus appropriate for the development of solid-phase versions for use in combinatorial synthesis (Scheme 18). 

Fluoroarenes from Anilines via a One-Pot, Thermal Reaction Using Hydrogen Fluoride-Oi anic Base Complex at the Dediazoniation Step General Procedure ... 

Table 10. Synthesis of Fluoroarenes from Anilines via Thermally Induced Decomposition of Complex Diazonium Fluoride Salts ...

Fluoroarenes from Anilines via Diazotization and Photochemically Induced Fluorodediazoniation in Hydrogen Fluoride-Organic Base Complex General Procedure 4 ... 

Scheme 2.45 Transition metal-mediated activation of the aromatic carbon—fluorine bond and subsequent reactions. Ahoue stoichiometric reaction of electron-deflclent fluoroarenes with NI(0) complexes [101]. Belou Ni(0) carbene-catalyzed Kumada-Corriu coupling between fluoroarenes and aryl Grignard compounds [102].

Oxidative addition of C-F bonds to low-valent metal complexes constitute one of the routes in activation of fluoroalkanes and fluoroarenes [71, 72], The chemical activation of carbon-fluorine bonds has attracted much attention since functionalization of C-F compounds gives various fluoroorganic derivatives, which have many technological applications. Typical examples of oxidative addition of C-F bonds [73] are shown in Scheme IV.36. 

Arenediazonium salts are converted to the corresponding fluoroarenes in the presence of boron trifluoride-diethyl ether complex. ... 

Hydroxylamines deprotonated by KOH substitute for chloride in (chloro-arene)Cr(C0)3 in high yields [24]. Reaction of a (fluoroarene)Cr(CO)3 complex with dialkyl phosphite 12 resulted in formation of a phosphate 13 [25]. The ar-ylation of oximes under phase transfer conditions leads to a simple process for benzofuran formation [26]. 

It has been found that ( 7 -fluoroarene)tricarbonylchromium complexes undergo Suzuki reactions with arylboronic acids to form (77 -biaryl)tricarbonylchromium complexes in the presence of PMe3/[Pd2(dba)3] and GsF or GS2GO3 (Scheme 43). Comparable Stille couplings have been developed. DFT calculations have been performed... 

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