Chloroarene complexes

More than twenty years ago, Nesmeyanov s group showed that chlorine can be substituted by a variety of nucleophiles in FeCp(r 6-PhCl)+ [83, 84]. Indeed the chlorine substituent in the chlorobenzene (even) ligand is 1000 times more reactive than when it is located on the cyclopentadienyl (odd) ligand [85]. The FeCp+ is a good withdrawing group which is equivalent to two nitro groups in terms of activation. The reactions proceed under ambient conditions with primary or secondary amines and have been extended to other substituted chloroarene complexes [86, 87] Eq. (22), Table 2. 

Similarly, Lee et al. have substituted the chlorine by azoturo in several chloroarene complexes [89, 90] Eq. (26), Table 4. 

Table 4. Yield of chlorine substitution by azoturo in chloroarene complexes...

A patent issued in 1965 claims substitution for fluoride on fluorobenzene-Cr(C0)3 in DMSO by a long list of nucleophiles [18]. Chloroarene complexes are typically less reactive [2]. The bromo- and iodoarene complexes are known,but generally are not effective in the S Ar reaction. The high reactivity of the fluor-obenzene complex allows nucleophilic substitution under mild reaction conditions. A variety of alkoxides [19] including chiral versions [20, 21] were used successfully. Alkyl sulfides replace fluoride in an analogous process [2,15, 22]. Several difluoroarene complexes are known and both fluorides can be displaced by a methoxide nucleophile [23]. 

Dichlorobenzene)FeCp reacts with diethylmalonate only once due to in situ deprotonation of the product addition of excess MeOH or methylthioglycolate allows disubstitution [66]. (Nitroarene)FeCp complexes have also been used with carbon nucleophiles [87] and again reactivity similar to the chloroarene complexes is observed. Application of carbon nucleophile substitution chemistry for the synthesis of heterocycles such as 36 is described [88]. 

An analogous polymer with diethynyldiphenylene spacers, 4.43, which possesses complexation of arene groups to Cr(CO)3 moieties, has been prepared [91]. Its solubility was low, even though molecular weights M ) of ca. 7800 were estimated. In this case, the synthesis involved a cross-coupling reaction of the p-di-chloroarene complex with the bis(trimethylstannyl)dialkyne [91]. Similar materials with diethynylthiophene spacers have also been described [92]. 

Polyaromatic ethers coordinated to CpFe+ moieties have also been prepared via sequential S Ar reactions of chloroarene complexes with hydroquinone (189). The electrochemical behavior of cationic aromatic ether, thioether, and sul-fone complexes of cyclopentadienyliron has been studied using cyclic voltammetry and coulometry (190). Reaction of the aromatic ether complexes with sodium cyanide resulted in the formation of neutral adducts which imder-went oxidative demetallation to give the corresponding organic aromatic nitriles (191). 

Nucleophilic aromatic substitution reactions of haloarenes complexed to transition metal moieties with oxygen-, sulfin-, and nitrogen-containing nucleophiles allows for the synthesis of a wide variety of aryl ethers, thioethers, and amines. These metal-mediated reactions proceed under very mild conditions and allow for the incorporation of a number of different functional groups. Nucleophilic substitution reactions of chloroarenes complexed to the cyclopentadienyliron moiety have been the focus of many studies directed toward the design of functionalized organic monomers. ... 

Complex 34 was subsequently reacted with the chloroarene complexes 36, 38, and 40, resulting in the isolation of star polymers 41 3 containing 9, 12, and 15 metallic moieties pendent to their backbones, respectively. The synthesis of these polymetallic stars is shown in Scheme 12. It was found that the solubility of these polymers decreased with increasing molecular weight however, all polymers could be solubilized in polar aprotic solvents such as DMF and DMSO. 

Nevertheless, the more practical chloroarene complexes are commonly used as they react well, whereas the activation by Cr(CO)3 is therefore not sufficient. 

C. Nucleophilic Aromatic Substitution Potymerization of Chloroarene Complexes... 

---