Iron tricarbonyl compounds

A similar phenomenon has been observed in the spectra of some diene-iron tricarbonyl compounds (136). The anisolechromium tricarbonyl complex shows loss of 2 H from the [M - 3 CO]+ ion, giving C7H6OCr+, which could have the tropone structure (XIV) while the analogous iso-propoxy complex loses propylene with the probable rearrangement to give... 

Some I F NMR parameters for (polyfluorocycloheptadiene)iron tricarbonyl compounds... 

In order to identify the structure of the polymer, we compared the spectral characteristics (IR/NMR) of this product with those of an appropriate octadiene derivative. Based on the work of Pettit, et al.- it would be predicted that octadienes could react with Fe(C0)5 to yield as many as six isomeric dienyl iron tricarbonyl compounds. 

The 3c-nmR spectrum of the thermal reaction product between 1,7-octadiene and FeCCO) (Fig. M) is complex and consists of 24 principal peaks which can only be accounted for in terms of the formation of a minimum of the six isomeric octadienyl iron tricarbonyl compounds shown in Fig. 2. While we have not unequivocally assigned each of these peaks, the eleven peaks at high field (14-40 ppm) are due to -CH and -CH2 carbons. The six peaks at (53-66 ppm) are mainly derived from the 1,4 carbons of the diene and the six peaks at 81-93 Ppm may be attributed to the 2,3 carbons of the diene. The low field doublet at 212 and 213 ppm derives from the carbonyl carbons and is indicative of two distinct carbonyl environments. 

The synthesis of the trismethylenemethane iron tricarbonyl complex [(CH2)3C]-Fe(CO)3 was reported by Emerson et al. in 1966 (27). The geometry of this compound in the gas phase was investigated by Almenningen et al. (28) using electron diffraction methods. These authors pointed out some structural peculiarities which were not amenable to a simple explanation, in particular, why the hypothetical planar (CH2)3C radical is distorted when bound to the Fe(CO)3 conical fragment in such a way that the carbon atoms of the CH2 groups are displaced toward — the iron atom (Fig. 9). 

Certain conjugated iron diene tricarbonyl compounds have been... 

Recently, in a study of a large number of organo-iron compounds 120), it has been found possible to treat the isomer shift as being due to a sum of partial isomer shifts 8,. from individual ligands which for 7r-cyclopentadienyl derivatives could be correlated with proton NMR chemical shifts in the same compounds. The Mossbauer spectra of two cases of theoretical interest are worthy of mention. First, the spectra of both the mono- and binuclear iron tricarbonyl derivatives of cyclooctatetraene 115) show similar 8 and A values. The small 8 values are consistent with zero oxidation state for the iron atom and essentially complete covalent bonding between the iron and the tt electrons of the ring, so that, at least for the mononuclear... 

An alternative preparation giving access to anfi-hydroxyvinyl compounds uses diastereo-selective nucleophilic addition to a chiral diene-iron tricarbonyl complex, followed by iodocarbamation and ring opening (Scheme 20)J75l... 

Although the diastereocontrolled cyclopropanation generally uses a chiral diazo compound, there is one exception in which a chiral olefin was used to react with an achiral diazo compound. Thus, copper catalysed cyclopropanation of chiral butadiene iron tricarbonyl complex 150 with methyl diazoacetate provided a 1 1 mixture of the trans (151) and cis (152) isomers (equation 132). The diastereomeric excess of both trans and cis are 90% and the decomplexation can be easily achieved by treating the adduct with trimethyl nitroxide in dichloromethane188. 

Azepines do not undergo electrophilic substitution reactions and introduction of substituents at the 3-or 4-position is a difficult problem. Acylation at C-3 can be achieved via the iron tricarbonyl complex as shown in Scheme 22.42 The N-ethoxycarbonyl group of the acylated product can be removed with methoxide methanol and the resulting 1H compound can then be methylated. 

My co-worker H. Beutner (95) was able to isolate from a nitrite-containing carbonylferrate solution, in trace amounts only, a binuclear nitrogen-atom-bridged iron carbonyl compound. This complex is now obtained in good yield by UV irradiation of the reaction solution and was identified mass spectrometrically as di-/x-amino-bis(tricarbonyl)iron, (OC)3Fe(NH2)2Fe (C0)3. The group... 

The mass spectra of some iron tricarbonyl derivatives of -ionone and related compounds (CVIII)-(CX) show the usual stepwise loss of CO groups from the molecular ion, but further analysis of the spectra was not attempted because of the complex nature of the ligands (36). Vitamin A... 

Apart from the di- and oligoolefm iron tricarbonyl complexes, which nowadays are frequently used in organic synthesis [71, 72], the chemistry of the readily accessible cyclohepatriene chromium and molybdenum tricarbonyls 2 and 3 was the focus of intense research efforts as well. Only a few months after the synthesis of 2 and 3 was published [58,59], both Hyp Dauben and Peter Pauson reported that these compounds react with triphenylmethyl tetrafluoro-borate in methylene chloride to give the tropylium complexes 4 and 5 in excellent yield (Scheme 7.1) [73, 74]. Later this method of hydride abstraction was also used for the preparation of the tropylium cation itself and subsequently led to the generation of several cationic rc-complexes of iron, manganese and cobalt [71, 72], The reactions of the cations of 4 and 5 with nucleophilic... 

Unsymmetrically substituted diene iron tricarbonyl complexes are formed as racemic mixtures of compounds having planar chirality. Optically pure diene iron tricarbonyl complexes can been prepared by classical chromatographic separation of diastereomeric mixtures of a-methylbenzylamine and ephedrine salts, and of semioxa-mazones and oxazohdines derivatives. Direct asyimnetric complexation to cychc dienes can be achieved 73% ee using iron pentacarbonyl in the presence of a chiral l-aza-1,3-butadiene. 

Oxidative removal of the iron tricarbonyl group can be achieved using iron trichloride, copper dichloride, CAN, hydrogen peroxide under basic conditions, 3-chloroperbenzoic acid, or TMANO. The latter oxidant is frequently the reagent of choice. Depending on the reagent, decomplexation may occur with or without concomitant transformation (Scheme 128). It is important to note that no racemization of optically active compounds is detected upon... 

Dienes coordinated to iron tricarbonyl do not undergo Diels-Alder reactions and a number of interesting annulation reactions of groups attached to iron tricarbonyl diene complexes have been developed. Cyclohexadiene iron tricarbonyl complexes having a pendant alkene undergo annulation reactions to form spirocychc compounds (Scheme 160). Related reactions of allylic thioesters afford spirocychc thialac-tones. 

The chemistry of diene iron tricarbonyl complexes described above has been in a number of total syntheses. An iterative stereospecific 1,3-migration of the iron tricarbonyl moiety was used to prepare compounds with multiple chiral centers. An example of one iteration can be seen in Scheme 168. Ester hydrolysis of (105) and protection of the resulting alcohol gives (106). Reduction of the nitrile with DIBAL-H followed by olefination furnished (107). Treatment of (107) with a base resulted in the migration of iron toward the nitrile to give (108). The uncomplexed double bond can... 

Hydride abstraction from dienyl tricarbonyl iron complexes furnishes cationic dienyl tricarbonyl iron complexes. For example, reaction of the diene-iron tricarbonyl complex (115) with triphenyhnethyl hexafluorophosphate followed by trimethylsilyl cyanide furnished with excellent regio- and stereoselectivity a new diene iron tricarbonyl complex (116) (Scheme 170). Excellent regio- and stereoselectivity is seen upon reaction of the cationic complex (116) with trimethylsilyl cyanide (TMS-CN) (Scheme 170). Reduction of the nitrile affords a spirocyclic lactam complex. Intramolecular cyclization of in situ formed enols furnishes spirocyclic compounds again with excellent stereoconfrol (Scheme 171). An interesting example of hydride transfer from a cyclohexadiene ring to a pendant aldehyde followed by nucleophilic addition is seen in Scheme 172. 

In 1959 a remarkable class of compounds containing cyclooctatetraene coordinated to iron tricarbonyl units was discovered independently by three research groups 165, 166, 182, 207). Two principal products were obtained having the compositions (C8H8)Fe(CO)3 and (C8H8)Fe2(CO)c, of... 

Polymercuration frequently occurs. The Hg atom is not large [the non-bonded radius is 1.50-1.73 A (150-173 pm), compared, e.g., with 1.95 A (195 pm) for Br], and its electronic effect is weak. Permercuration of aromatics is possible, and not all compounds require drastic conditions, such as fusion with reactive Hg salts . Furan , pyrrole , thiophene and cyclobutadiene iron tricarbonyl are mercurated under mild circumstances. For the monomercuration of the more reactive aromatics, the extent of reaction must be limited, e.g., by using the mild HgCl2 in the presence of Na02CCH3 to buffer the solution. 

I was first made aware of organometallic compounds through reading Modern Aspects of Inorganic Chemistry (1935) by two academics, H. J, Emeleus and J. S. Anderson at Imperial College, London, where I was a student. However, names such as Zeise s compound , Reihlen s butadiene iron tricarbonyl and Hein s polyphenylchromium compounds , none of whose structures were known, remained latent in my memory through over seven years as a nuclear chemist. 

Lithium alkynylcuprates react with haloallenes to give similar skipped diacetylenes (see below). The related skipped enynes can be prepared by treatment of (pentadienyl)iron(tricarbonyl) halide complexes with dilithium trialkynylcuprates, the compounds being isolated as the iron(tricarbonyl)(diene) complexes (Scheme 4). Further examples of alkylation reactions of copper alkynides are illustrated in Scheme 5. Reaction between a lithium cyanoaikynecuprate and an iodoallene leads to a skipped diacetylene. This useful reaction has been used by Corey in his synthesis of hybridalactone (Scheme 6). °... 

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