IRON , TRICARBONYL

Cyclo-octatetraene-iron tricarbonyl (A) was originally isolated from the reaction mixture of cyclo-octatetraene and iron pentacarbonyl. The properties of A are as follows UV, 303 increasing absorption at shorter 

From the limited data above, the tentative structures [5-39] and [5-40] can be proposed. However, A does not absorb hydrogen even in the presence of active hydrogenation catalysts such as platinum or palladium, which would be expected to happen if two olefinic bonds were uncomplexed. 

The iron tricarbonyl group is attached to a butadiene unit of the cyclo-octatetraene ligand. This structure was simply ignored by early investigators. 

At present it is understood that cyclo-octatetraene iron tricarbonyl may have a different structure in solution than it does in the crystalline state. Indeed, different protons are detected at different temperatures, which has led to such descriptions as ring whizzing, dynamic equilibrium, and stereochemical nonrigidity in an attempt to describe the bonding. 

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Chiral diene—iron tricarbonyl complexes were acylated using aluminum chloride to give acylated diene—iron complexes with high enantiomeric purity (>96% ee). For example, /ra/ j -piperjdene—iron tricarbonyl reacted with acyl haUdes under Friedel-Crafts conditions to give l-acyl-l,3-pentadiene—iron tricarbonyl complex without any racemization. These complexes can be converted to a variety of enantiomericaHy pure tertiary alcohols (180). 

A yellow crystalline complex (2) melting at 198°C is formed from sorbic acid and iron tricarbonyl (10) ... 

Stabilization of Unstable Intermediates. Transition metals can stabilize normally unstable or transient organic intermediates. Cyclobutadiene has never been isolated as a free molecule, but it has been isolated and fully characterized as an iron tricarbonyl complex (138) ... 

The reactivity sequence furan > tellurophene > selenophene > thiophene is thus the same for all three reactions and is in the reverse order of the aromaticities of the ring systems assessed by a number of different criteria. The relative rate for the trifluoroacetylation of pyrrole is 5.3 x lo . It is interesting to note that AT-methylpyrrole is approximately twice as reactive to trifluoroacetylation as pyrrole itself. The enhanced reactivity of pyrrole compared with the other monocyclic systems is also demonstrated by the relative rates of bromination of the 2-methoxycarbonyl derivatives, which gave the reactivity sequence pyrrole>furan > selenophene > thiophene, and by the rate data on the reaction of the iron tricarbonyl-complexed carbocation [C6H7Fe(CO)3] (35) with a further selection of heteroaromatic substrates (Scheme 5). The comparative rates of reaction from this substitution were 2-methylindole == AT-methylindole>indole > pyrrole > furan > thiophene (73CC540). 

Germacyclopentadie ne, 1 - exo-fl uoro-1 -methyl-2,3,4,5-tetraphenyl-iron tricarbonyl complex structure, 1, 617 Germacyclopentane, 1-phenyl-bromination, 1, 607 Germacyclopentanes, 1, 605-609 chemical properties, 1, 607-608 synthesis, 1, 605-607 Germacyclopentenes synthesis, 1, 610-612 Germacyclopent-3-enes properties, 1, 612 reactions... 

The reaction of o-diphenylcyclobutadiene (generated in situ by oxidation of its iron tricarbonyl complex) with p-benzoquinone yields A as the exclusive product. With tetracyanoethylene, however, B and C are formed in a 1 7 ratio. Discuss these results, and explain how they relate to the question of the square versus rectangular shape of cyclobutadiene. 

The double bond transposition could also be achieved by the conversion of an intermediate for PGA2 synthesis into a 1,3-diene iron tricarbonyl complex from which PGC2 was synthesized in four steps. The Fe(CO)3 diene complex which survived the Wittig reaction was cleanly removed by Collins reagent in the subsequent step (Ref. 10). 

In the complexes of 1,3-boroles containing the unsaturated substituents (89CB633, 90CB2273, 94CB2393), the coordination mode is in the case of iron tricarbonyl complexes 10 and 11 (R = H, Me). 

Isopropyl l//-l,2-diazepine-l-carboxylate similarly gives tricarbonyl(4-7t/-l-isopropoxycar-bonyl-l//-1,2-diazepine)ironin45% yield (mp 106"C)and l-acetyl-3-methyl-l//-l,2-diazepine gives the corresponding iron tricarbonyl complex in 92% yield (mp 110 C).77... 

Ethyl 5-methyl-l//-l,2-diazepine-l-carboxylate and its 5-phenyl analog do not yield iron tricarbonyl complexes.77... 

Iron Tricarbonyl Complexes 19-21 of l-Troponyl-l//-l,2-diazepines and Their Decomplexation to 1-Tro-ponyl-127-1,2-diazepines 22-24 ... 

An iron tricarbonyl complex 19-21 (0.338 g, 1 mmol) and freshly sublimed Me3NO (0.6 g, 8 mmol) in acetone was left at rt for 4h. Evaporation, followed by flash chromatography (alumina, Et20), gave the corresponding unstable l-troponyl-l//-l,2-diazepines 22-24 in 76, 76 and 44% yield, respectively. 

Table 2. Values of OC—Fe—CO bond angles in the iron tricarbonyl group ...

Birnbaum, G. I. (1972) Structure of the unsymmetrical 12-oxa[4.4.4jpropella-2,4,7,9-tetraene bis(iron tricarbonyl). An example of an oxygen-diene interaction through space, J. Am. Chem. Soc. 94,2455-2459. 

In a number of cases, alkenes that are too unstable for isolation have been isolated in the form of metal complexes. As example is norbomadienone, which was isolated in the form of its iron-tricarbonyl complex (11). The free dienone spontaneously decomposes to carbon monoxide and benzene (see 17-29). 

Iron tricarbonyl dieme complex, 57, 16 Isobutyl chloroform.ate, 59, 165 Isobutylene, 59, 164 Isobutyl fluoride, 5, 73 Isobutyryl chloride, 59, 29 Isocyanato acid chlotrides, from amino acids, 59, 200... 

Whitesides TH, Shelly J (1975) Thermolysis and photolysis of (cyclopentadiene)iron tricarbonyl. Evidence for a radical mechanism involving iron(I). J Organomet Chem 92 215-226 Shackleton TA, Mackie SC, Fergusson SB, Johnston LJ, Baird MC (1990) The chemistry of (r -C5H5)Fe(CO)2H revisited. Organometallics 9 2248-2253... 

Benzocyclobutene, when generated by oxidation of its iron tricarbonyl complex, can function as the dipolarophile in 1,3-dipolar cycloaddition reactions with arylnitrile oxides (Scheme 113).177 Unfortunately the synthetic versatility of this type of process is limited because of the unreactivity of other 1,3-dipolar species such as phenyl azide, benzonitrile N-phenylimide, and a-(p-tolyl)benzylidenamine N-oxide.177... 

Rather than focusing on the short-time photochemical reactivity, our interest in the spin-forbidden reactions of iron carbonyl fragments has been mainly in the longer-time thermal chemistry of the fragments produced. This is summarized in Scheme 3. As already stated, iron tricarbonyl and tetracarbonyl are known to have triplet ground states, and for many ligands, it is assumed that Fe(CO)3L would also have a triplet ground state. Hence many of the indicated processes are spin-forbidden. 

Fragments derived from photolysis of Fe(CO)s have been observed to catalyze olefin isomerization and hydrogenation (65-67). The key active species for the isomerization is iron tricarbonyl which can easily add alkene to give Fe(CO)3(alkene). 

Photolysis of Fe(C0)4L species can lead to loss of CO, with formation of Fe(CO)3(L), and the latter can also be formed, as just discussed, by addition of L to iron tricarbonyl. In this section, we discuss the kinetics of addition of a second ligand L to form singlet species of general formula 1Fe(CO)3(L)(L ). We consider three cases addition of CO to 3Fe(CO)3(H2), and addition of CO or ethylene to Fe(CO)3(C2H4). 

The oxidative cyclization of chiral 2-pyrrolidino-l-ethanol derivatives is shown in the reaction of 251 with trimethyl-amine iV-oxide and a substoichiometric amount of cyclohexadiene iron tricarbonyl to produce the corresponding oxazolopyrrolidine ring 252. The mechanism of this reaction is unknown. Both amine oxide and iron complex are essential for the reaction (Equation 39) <2005TL3407>. 

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). 

Other than this system, metallated polysilanes contain the metal in low-valent oxidation states. Such systems have been reported by two groups. In 1995, an alternative functionalization route starting from poly[methyl(H)silylene] or poly[methyl(H)silylene-fo-methylphenylsilylene], 37, was reported, in which the polysilane Si-H moiety was hydro-silated using 1,3,5-hexatriene, affording the diene-modified polymer 67, which was metal functionalized using triiron dodecacarbonyl to give the iron tricarbonyl-polysilane coordination complex, 68.177... 

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