Iron carbonyl complexes, cationic

Heterocyclic phosphonium salts, e.g., (105), have been prepared by the reactions of urea-bridged P,P-dipho8phines with methyl triflate. - - Two ehantiomeric iron carbonyl complexes of the butadienylphosphonium salt (106) have been obtained by the trapping of a complexed organic cation with triphenylphosphine. ... 

Transition metal catalysts, specifically those composed of iron nanoparticles, are widely employed in industrial chemical production and pollution abatement applications [67], Iron also plays a cracial role in many important biological processes. Iron oxides are economical alternatives to more costly catalysts and show activity for the oxidation of methane [68], conversion of carbon monoxide to carbon dioxide [58], and the transformation of various hydrocarbons [69,70]. In addition, iron oxides have good catalytic lifetimes and are resistant to high concentrations of moisture and CO which often poison other catalysts [71]. Li et al. have observed that nanosized iron oxides are highly active for CO oxidation at low tanperatures [58]. Iron is unique and more active than other catalyst and support materials because it is easily reduced and provides a large number of potential active sites because of its highly disordered and defect rich structure [72, 73]. Previous gas-phase smdies of cationic iron clusters have included determination of the thermochemistry and bond energies of iron cluster oxides and iron carbonyl complexes by Armentrout and co-workers [74, 75], and a classification of the dissociation patterns of small iron oxide cluster cations by Schwarz et al. [76]. 

Kovacs, I. Baird, M.C. (1995) Neutral and cationic iron carbonyl-complexes substituted with the water-soluble phosphines Ph2P(CH2) PMe3 ( = 2, 3, 6 and 10), J. Organomet. Chem., 502,87-94. 

Other interesting uses of iron carbonyl complexes include the synthesis of N-substituted l//-l,2-diazepine (95) and the synthesis of cyclic hydrocarbons (96) via intramoleculai coupling of bis-pentadienyl iron tricarbonyl cations. 

Iron carbonyl complexes containing 77 -alkyl-77 -allyl coordinated hydrocarbon ligands are obtained in several ways. Nucleophilic addition to cationic iron complexes containing 77 -pentadienyl ligands yields (pentenediyl)iron complexes. Oxidatively-induced reductive elimination of these complexes can be utilized as a means to generate 1,2,3-trisubstituted cyclopropanes.The reaction of cationic cycloheptadienyl complexes (Scheme 22) with appropriate nucleophiles also yields the alkyl-allyliron carbonyl complexes. Fe(CO)s also reacts with a- or /3-pincnc in refluxing dioxane (Scheme 22) to produce an alkyl-allyliron complex. Recently, 1,2- and 1,4-disubstituted [(pentadienyl)Fe(CO)3] cations were shown to react with carbon nucleophiles, such as sodium dimethylmalonate, to yield 77 77 -allyl complexes as products. 

The reactions of various iron carbonyl complexes, such as Fe(GO)4(NMe3), with allene compounds under photo-lytic conditions, yield chelated 77 -allyliron complexes. Two brief reviews discussing the chemistry and application to organic synthesis of these (7r-allyl)tricarbonyl iron lactone complexes have appeared recently. Reaction of the iron lactone complexes with trimethyloxonium tetrafluoroborate yields the carbene complex 23 in good yields. Treatment of the cationic carbene complex with triphenylphosphine results in substitution at the terminal end of the allyl ligand of the trimethylenemethane complex 24. 

Since 1958 a considerable amount of research activity has centered around these systems, both in the acetylene-iron carbonyl reactions and the direct reactions of olefins with iron carbonyls. The types of unsaturated ligands which are now known to occur in stable iron carbonyl complexes include substituted and nonsubstituted cyclic, acyclic, and nonconjugated dienes as well as some aromatic systems. Furthermore, what may be formally regarded as dienyl cations as well as allyl cations and radicals are found to... 

The reaction between the allylic bromide (37) and Fe(CO)s constitutes an alternative method of preparation of tricarbony 1( 1,3-cyclohexadiene)iron (38) (eq 16). Allylic alcohols react in a similar way (eq 17) under neutral conditions, but in the presence of acid (HBF4), cationic iron carbonyl complexes are produced. ... 

We synthesized cationic y2-acetyl compounds 28,25 by combining iron acetyl complexes CpFe(C0)L(C0CH3) (g7) [L=C0,PPh3] with a coordinatively unsaturated (16-electron) metal carbonyl salt CpM(CO)n+[M=Fe,n=2 M=Mo,n=3], as indicated in Scheme 5. Thus... 

Several factors must be taken into account when the dispersion of iron catalysts prepared by carbonyl complexes is compared to that of conventionally prepared catalysts. The iron loading and the possible formation of irreducible iron phases (by the interaction of Fe or Fe with the support) can determine a low reduction degree for conventionally prepared catalysts with low iron content and a support with high ability to react with the iron cations. In contrast, when catalysts prepared from carbonyl complexes are considered, for a given support the temperature of pre treatment which defines the hydroxyl population of the surface is a main aspect to be taken into account. For Fe/Al203 catalysts prepared from iron carbonyls and reduced after impregnation at a moderate temperature (573 K), the extent of... 

Ring enlargement to r/3-oxocyclobutenyl complexes, by carbonyl insertion into the three-membered ring, is generally observed in reactions of group 9 cobalt carbonyl anions with cyclopropenylium cations (equation 197)271 275. Formation of j/ -oxocyclobutenyl complexes also occurs with nitroso iron carbonyl anions270,275. These reactions are usually... 

The analogous cycloheptadienyl complex (5 equation 1) was similarly prepared by Dauben and Ber-telli,4 but the acyclic pentadienyl systems were a little more difficult to obtain. The triphenylmethyl cation does not remove hydride from tricarbonyl(frans-pentadiene)iron (6 equation 2). The corresponding c/s-pentadiene complex (7 equation 3) cannot be prepared directly from the diene and an iron carbonyl,... 

The cyclopropanation reactions of the cationic iron carbene complexes occur most efficiently with alkenes of normal electronic characteristics. Veiy electron deficient alkenes such as a,(3-unsaturated carbonyl compounds are veiy poor substrates. Veiy electron rich alkenes such as enol ethers react rapidly, but the expected cyclopropanes generally cannot be isolated if they are indeed formed, they apparently undergo further reactions, peihaps promoted by the metallic species present in the reaction mixtures. 

Similarly protonation of diphenylfulveneiron tricarbonyl generates a substituted 7r-cyclopentadienyl cation (241, 242). Hydride abstraction from cyclopentadieneiron tricarbonyl releases the 77-cyclopentadienyl cation complex (172). The Mossbauer spectra of the [CpFe(CO)3]1 cation and related iron carbonyl cations have been determined (121). 

Fe(NH3)6]Br2 When an excess of gaseous ammonia is passed through a freshly prepared solution of elemental iron in hydrobro-mic acid (40%), the bromide salt of the hexaammine iron(II) complex is deposited (86). The cation is also found in certain carbonyl ferrates, such as [Fe(NH3)6][Fe3(CO)u], which are obtained from the reaction of triiron dodecacarbonyl with ammonia in an autoclave (87). 

The carbonyl complex 33 is obtained in a clean displacement reaction when carbon monoxide is passed through a solution of 32 in methanol. Due to the increased charge on the cation, the product precipitates in the process. The rather low frequency of the C O stretching vibration in the IR spectrum of the solid (KBr disc) at 1960 cm-1 points to a strong Fe-CO interaction (100), as expected for the highly basic NN4 ligand environment. Similarly low values (1940-1960 cm-1) were reported for the pentaamine iron(II) complexes... 

Iron complexes can also catalyze allylic amination [31,32]. Enders et al. have demonstrated the nucleophilic addition of various acyclic and cyclic amines to the optically active l-methoxycarbonyl-3-methyl-(T)3-allyl)-tetracarbonyliron cation 49 formed in high yield from reaction of 48 with iron carbonyls. Oxidative removal of the tetracarbonyliron group by reaction with CAN gives 50 with high optical purity and retention of the stereochemistry (Eq. (12)) [31]. The reaction proceeds well for the different amines, and has been used for the synthesis of a compound showing cytotoxic activity against diverse cell lines [31b]. 

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