Arene-Iron Complexes

Two types of arene-iron complexes are known in the literature, monocationic arene-FeCp and dicationic bis(arene)Fe complexes [75]. The former type is more stable and shows a more useful chemistry. Arene-FeCp complexes can be prepared... 

Dicationic bis(arene)iron complexes are prepared from Fe(II) salts using the corresponding arene as solvent in the presence of aluminum trichloride at elevated temperatures. Because of the double positive charge, they easily add two nucleophiles at one arene ring. 

A new approach for the generation of NHCs has been reported using a cyclopentadi-ene(arene)iron complex (17).22 The method converts imidazolium to the free carbene in the presence of oxygen (peroxyradical anion is the base deprotonating the imidazolium salt). A colour change and precipitation of the oxidized iron complex are evidence for the reaction outcome. 

Nesmeyanov, Volkenau et al. were the first to replace cyclopentadienyl with another ligand in ferrocene, preparing cyclopentadienyl-arene iron complexes by reaction of ferrocene with aromatic compounds in the presence of AICI3 255-259). 

The iron vapor-toluene reaction has evoked interest because of the lability of the proposed bis(arene)iron complex to ligand subsitu-tion and to loss of both toluene molecules to free the metal atom. In the latter case the toluene molecules may be usefully regarded as metal atom carriers which can be used to direct the latent reactivity of the atom in subsequent solution phase chemistry. In this way the metal atom experiment can benefit from the convenience and additional versatility afforded by bench-top chemical manipulations. These results are relevant to a reported preparation of a dehydroxy-lated silica-supported Fischer-Tropsch catalyst from a static reactor codeposition of Fe and toluene.(46) In the liquid phase, iron atoms "bottled" in this way have also been utilized in an exceedingly mild method for making minute catalytically active superparamagnetic clusters on the surface and within the cavities of a dehydrated sodium zeolite Y.(38) Using the rotary reactor, preformed solutions of solvated iron atoms (as the toluene complex) are cannulated below their decomposition temperature out of the flask to a cold slurry of the support in toluene. Diffusion of intact... 

The classic method of preparing bis( j -arene)iron complexes by reacting the arene with FeClj/AlClj is not directly transferable to cyclophanes, because they, even in the presence of traces of HAICI4, isomerize [91]. However, after addition of Me3Al2Cl3 (method g) as a proton scavanger the bisiron complex 107 is formed [79] as an orange solid which is sensitive towards oxidation in solution and in the solid state (Fig. 23). Methyl substituted cyclophane ligands provide stabilization to some extent [92]. 

Iron carbonyl complexes containing tin(ll) ligands could also be obtained starting from arene iron complexes by displacement of the arene (Equations (49) and (50))4 Reactions of (arene)Fe(SnR2)(ethene) or bis bis(2- /t-butyl-4,5,6-trimethylphenyl) Sn Fe( -toluene) with carbon monoxide led to the substitution of the ethene and toluene ligands (Equation (49))4 The complex bis bis(2- /ir-butyl-4,5,6-trimethylphenyl) Sn Fe( j -toluene) was synthesized and reacted with 1 atm of carbon monoxide (Equation (50)). Attempts to synthesize the product in which only the toluene is substituted were unsuccessful. 

The interaction of aromatic hydrocarbons with iron cations has been studied in the gas phase. The results of these studies provide information useful in the proposal that polycyclic aromatic hydrocarbons undergo efficient reactions with iron and other transition metals in the interstellar medium. Fe(r/-G2H4)2(r7-PhMe) 87 is a useful precursor for a range of arene iron complexes. Thus, reaction of 87 with the desired naphthalene derivative and three molecules of butyne or hexyne leads to the (hexaalkylbenzene)naphthalene iron complexes, as shown in Scheme 15. ... 

Trimerization of alkynes to form aromatic compounds has been achieved first by Reppe and Schweckendiek using nickelcarbonyl complexes as catalysts. The applicability of carbonyliron complexes for this purpose was reported as early as 1960. Unsymmetric acetylenes give exclusively the arenes with symmetric substitution pattern under these conditions (Scheme 4-309). Alternatively, (Ti -arene)iron complexes such as bis(ethene)(toluene)iron can be used for the cyclotrimerization of unsymmetric alkynes. A variety of symmetrically substituted benzene derivatives has been obtained. Another very active precatalyst for this reaction is (Ti -cyclohepta-l,3,5-triene)(T -cycloocta-l, 5-diene)iron(0). ... 

Bis-arene iron dications [20] are easily accessible from arenes, A1C13 and FeCl3 (for C6Me6, FeCl2 must be used). It is advisable to use tris-sublimated A1C13 to avoid problems of isomerization [23], With toluene, this isomerization due to the re/ro-Friedel-Crafts mechanism [24] is too extensive to give any clean complex. 

Mixed arene-2,5-dihydro-l,2,5-thiadiborole-iron complexes have been synthesized by a novel route thermally unstable bis(arene)iron sandwich complexes, prepared by cocondensation of iron atoms with arene, react in the temperature range of -100 to -60°C with free Et2C2B2Mc2S to form reactive intermediates that decom-... 

Scheme 7 Intramolecular arene coordination in bis(imino)pyridine iron complex 10...

Abstract In this review, recent developments of iron-catalyzed oxidations of olefins (epoxidation), alkanes, arenes, and alcohols are summarized. Special focus is given on the ligand systems and the catalytic performance of the iron complexes. In addition, the mechanistic involvement of high-valent iron-oxo species is discussed. 

Decomplexation of some metal complexes calls for drastic conditions. This is true for (/7-arene)(/7-cyclopentadienyl)iron(II) hexafluorophosphates, [FeAr(Cp)][PF6] [54, 55]. Although their chemical decomplexation is known [55 a], the most widely used method is pyrolytic sublimation at high temperatures (>200 °C) [55 b]. To evaluate MW irradiation as the method of decomplexation of such iron complexes, Roberts et al. performed the reaction in the presence of graphite [54]. They discovered that the yield of the free ligand from the [Fe( -N-phenylcarbazole)( -Cp)][PF6] complex (43) depended on the kind (flakes or powder) and amount of graphite, and on the irradia-... 

Carbocations as electron acceptors in aromatic EDA complexes 192 Bis(arene)iron(II) complexes with arene and ferrocene donors 198 Carbonylmetallate anions as electron donors in charge-transfer salts 204 Aromatic EDA complexes with osmium tetroxide 219... 

BIS(ARENE)IRON(II) COMPLEXES WITH ARENE AND FERROCENE DONORS... 

Photoactivation of the bis(arene)iron(II) complexes with ferrocene and arene donors by the selective irradiation of the charge-transfer absorption bands as in (6) uniformly results in the de-ligation of the acceptor moiety... 

The formation of the monocationic intermediate (ArH)2Fe+ attendant upon the charge-transfer excitation of either the ferrocene or methylan-thracene EDA complex (7a and 7b) is responsible for the photo-induced de-ligation of bis(arene)iron(II), as described in (6). Thus, transient electrochemical studies (Karpinski and Kochi, 1992a,b) show that the catalytic de-ligation of (ArH)2Fe+ proceeds rapidly via a (two-step) electron-transfer chain or ETC process (8). 

As well as organic chiral auxiliaries, organometallic fragments have found some application as chiral auxiliaries in conjugate addition reactions. Particularly noteworthy are chiral molybdenum allyl complexes [69], chiral iron complexes [70], and planar chiral arene chromium species [71]. 

Aquocoppert I) complexes, 17 117, 118 Aquoxides, 5 215 Archibald technique, 19 256 Arenecyclopentadiene-iron complexes, 4 92 Arenediazo complexes, from oxomolybdenum complexes and hydrazines, 23 225-226 h -Arene ligands, osmium, 37 244 Arenes... 

Reduction of arene-Tr-cyclopentadienyliron(II) cations, which are iso-electronic with the di-ir-cyclopentadienylcobalt cation, with lithium aluminium hydride yields the neutral arenecyclopentadiene-iron complexes (100) ... 

Reactions of cobalt and nickel atoms with toluene and other arenes yield condensates in which the metal is in a very reactive state (105). However, none of the products of reaction of these condensates with other ligands has contained the arene coordinated to the metal. It seems possible that the condensates contain ditoluenecobalt and ditoluene-nickel, but in these complexes (unlike the chromium or iron complexes) the two arene rings are probably not symmetrically bonded to the metals. 

Reaction of Resin-Bound Iron Complex (54) with Alkyl Mercaptans, Thiophenols, and Phenols (Fig. 9)31. Sodium thiolates are prepared analogously to the alkoxides from thiol and sodium hydride, except that dry DMF is used as a solvent. The substitution on the polymer-bound arene (54) is performed at 70° in DMF within 16 h. The resin is filtered and washed with DMF (2 x 50 ml), MeOH (2 x 50 ml), H20 (2 x 50 ml), MeOH (2 x 50 ml), and CH2CI2 (3 x 50 ml) and then dried in vacuo at 40° to yield a red resin. 

Bis(arene)hafnium complexes, characteristics, 4, 697 Bis(arene)iron dications, characteristics, 6, 173 Bis(arene)niobium complexes, characteristics, 5, 95 Bis(arene)titanium(0) complexes, characteristics, 4, 243-244 Bis(arene)tricarbonylchromium complex, synthesis, 5, 258... 

The use of transition-metal arene complexes to facilitate nucleophilic aromatic substitution features in a route to derivatives of thiosalicylic acid and hence to thioxanthone. The cyclopentadienyl iron complex of 2-chlorobenzoic acid is converted into the benzamide prior to displacement of the chloride by thiophenoxide. Photolytic decom-plexation followed by directed remote metallation of the diaryl sulfide yielded the heterocycle (Scheme 207) <2000SL975>. 

The octasubstituted cored dendrimer 24-FeAr containing 24 cationic aminoarene iron moieties [dendr-( 6-NHC6H4MeFeCp )24] (Cp = rj5-CsMes), i.e. eight tripods, was compared to the analogous mono- and trimetallic amino-arene cationic complexes (resp. 1-FeAr and 3-FeAr, Scheme 9 and Fig. 12) with the same amino-arene iron-sandwich structure for the... 

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