4- -1,3-cyclohexa diene iron tricarbonyl

Shortly afterwards, in 1960, Fischer discovered that addition of triphenyl-carbenium tetrafluoroborate to T -cyclohexa- 1,3-diene iron tricarbonyl 4 produced the novel in -cyclohexadienyl iron tricarbonyl cation 5 as a stable salt, and the reactivity of such compounds towards C-C bond formation was soon being explored. The application of organometallic complexes to organic synthesis had begun. 

Reports on the synthesis of diene complexes using Fe2(CO)9 are more common. Reaction of 2-phenylsulfonyl-1,3-cyclohexadiene with 2equiv. of Fe2(GO)9 in refluxing ether formed the [l-(phenylsulfonyl)-l,3-cyclohexa-diene]iron(0)tricarbonyl isomer 26. The reaction is catalyzed by 1-aza-1,3-butadiene. In a separate study, 1-aza-1,3-butadienes were shown to effect a quantitative catalytic complexation of cyclohexadienes with Fe2(GO)9. Activities are greatly enhanced in the presence of aryl rings bonded to nitrogen. 

Some reactions of cyclohepta- and cyclohexa-dienyl iron tricarbonyl complexes resemble the reactions of the jr-cyclopentadienyl iron analogues. However, ring addition reactions which give diene derivatives occur more readily [263c], e.g. 

The complexation of 2b in the presence of 12.5 mol% of the azadiene catalyst 4 provides quantitatively tricarbonyl[r] -cyclohexa-l,3-diene]iron 5... 

An alternative method for the oxidative cyclization of the arylamine-substituted tricarbonyl(r -cyclohexa-l,3-diene)iron complex (725) is the iron-mediated arylamine cyclization. Using ferricenium hexafluorophosphate in the presence of sodium carbonate provided hyellazole (245) directly, along with the complex 727, which was also converted to the natural product (599,600) (Scheme 5.71). 

The structure of the complex formed from tricarbonyl(isoprene)iron and hexafluoropropene has been established crystallographically as [77], allowing the assignment of the parameters shown with the structure, and similar assignments for the products from the butadiene- and 2,3-dimethylbutadiene-tricarbonyliron complexes then follow. (49) With tricarbonyl(cyclohexa-l,3-diene)iron, hexafluoropropene gave [78], in... 

Iron tricarbonyl complexes of 1,3-dienes (e.g. cyclohexa-1,3-diene) play an important role in organic synthesis the complexes are stable under a variety of reaction conditions, and iron carbonyls are inexpensive. The Fe(CO)3 group acts as a protecting group for the diene functionality (e.g. against additions to the C=C bonds), allowing reactions to be carried out on other parts of the organic molecule as illustrated by reaction 23.87. 

As with acyclic dienes, methods have been developed for enantioselective and diastereoselectlve complexation of prochiral and chiral cyclic dienes. An approach has been developed for the asymmetric catalytic complexation of prochiral cyclohexa-1,3-dienes using (1) in the presence of catalytic amounts of 1-azabuta-l,3-dienes such as (232) or (233) an enantiomeric excess as high as 86% has been reported.By contrast, attempts to effect diastereoselective complexations using cyclic diene systems equipped with chiral auxiliaries have met with limited success. " On the other hand, direct complexation of chiral cyclic dienes such as (234) and (235) proceed with a high degree of diastereoselectivity, where the iron tricarbonyl fragment is directed syn to alcohols or ethers by transient coordination ( heteroatom delivery ) (Scheme 66). ... 

An -ray structure determination of a cationic intermediate (8) isolated during the acylation of [Fe(CO)8(rraAw, ra j-hexa-2,4-diene)] establishes that Friedel-Crafts acylation involves stereospecific endo attack. The stereochemistry of reaction parallels protonation of tricarbonyl(diene)iron, cyclopentadienyl(cyclohexa-l,3-diene)rhodium complexes, and ( j -cyclopentadienyl)rhodium complexes of limonene (9), a-phellandrene (10), and carvone (11). ... 

Iron tricarbonyl complexes of 1,3-dienes (e.g. cyclohexa-1,3-diene) play an important role in organic synthesis. The complexes are stable under a variety of reaction conditions. 

Interestingly, a ir-bonded organometallic complex had been synthesised long before ferrocene. In 1930, Reihlen and fellow German co-workers reported that the reaction between Fe(CO)5 and butadiene produced a yellow oil that analysed as C4H6Fe(CO)3. Structure 3 was tentatively suggested for this compound. However, it was not until 1958 that the true nature of this material was realised when Pauson and Hallam synthesised an iron tricarbonyl complex of cyclohexa- 1,3-diene and put forward evidence to favour the planar structure 4, in which the ir-orbitals are utilised in the bonding. ... 

Fundamental to the development of dienyl iron tricarbonyl chemistry has been the availability of substituted cyclohexadiene precursors arising from the Birch reduction. In this process, a wide range of aromatic compounds are readily reduced to their corresponding unconjugated cyclohexa-1,4-dienes without further reduction to a cyclohexane. The reaction is typically performed by adding sodium to a liquid ammonia solution of the substrate in the presence of an added alcohol. 

Charge one of the flasks with the crude tricarbonyl(1-methoxy-4-methyl-cyclohexa-1,3-diene)iron (5.0 g, 0.019 mol) prepared in Protocol 8, add a septum to the open neck and label as flask A. 

Grubb s ruthenium carbene catalyst to afford medium-sized carbocycles (Equation (10))." Iron tricarbonyl systems containing diazoketones tethered to the terminal position of the acyclic coordinated diene have been utilized to effect ring formation, via inter- and intramolecular carbene reactions, affording new cyclohexa-2,4-dienone and cyclopent-2-enone tricarbonyl iron complexes. ... 

Dimethyl(phenyl)silyllithium can be added as a nucleophile to the tricarbonyl(ri -cyclohexa-l,3-diene)iron complex. Quenching the reactive intermediate with trifluoro acetic acid provides l-dimethyl(phenyl)silylcyclohex-l-ene, whereas treatment with 2-(phenylsulfonyl)-3-phenyloxaziridine affords predominantly the corresponding [r) -2-dimethyl(phenyl)silylcyclohexa-l,3-diene]iron complex as the major product... 

The dynamic diastereoselectivity during the [6+2] ene spirocyclization of a mixture of two enantiopure diastereoisomeric allylamide-tethered tricarbonyl(T -cyclohexa-l,3-diene)iron complexes leads to only two diastereoisomeric spirolactams out of four possible isomers. A double cyclization of tricarbonyl(T) -cyclohexa-l,3-diene)iron complexes with pendent conjugated dienes gives rise to tricyclic (diene)iron complexes. Four new stereogenic carbon centers are formed in the course of this reaction to give a single diastereoisomer (Scheme 4-124). ° ° ... 

Tricarbonyl(ri -cyclohexa-l,3-diene)iron complexes are intermediates in the reaction of tricarbonyI(T -cyclohexadienylium)iron complexes with substituted anilines in the presence of air (Scheme 4-131). Under these conditions, concomitant oxidative cyclization of the intermediate aniline-functionalized (ri -cyclohexa-l,3-diene)iron complexes occurs to give tricarbonyliron-complexed dihydrocarbazoles. The latter are... 

A solution of tricarbonyl(ri -cyclohexa-l,3-diene)iron (11.5 g, 52.4 mmol) in dichloromethane (70 mL) is added to a solution of triphenylmethyl tetrafluoroborate (20.8 g, 62.9 mmol) in dichloromethane (70 mL). The reaction mixture is stirred for 40 min at room temperature and then poured into wet diethyl ether (700 mL). The resulting... 

Starting from a cisoid 1,3-diene, Fe2(CO)9 can yield, under mild thermal conditions, tricarbonyl(T -l,3-diene)iron complexes. Cyclohexa-1,4-dienes (readily available from the Birch reduction of substituted benzenes) often require prior conjugation, but conjugated 1,3-dienes (both cyclic and acylic) can be converted into tricarbonyliron complexes directly. Some of the earliest examples " of complexation of 1,3-dienes employed Fe2(CO)9 (eq 3, dates shown in parentheses). (Alternative reagents in the early days were Pentacarbonyliron or Dodecacarbonyltriiron.)... 

Starting material for this synthetic strategy is tricarbonyl(ri -cyclohexadieny-lium)iron tetrafluoroborate 30, which can be prepared from cyclohexa-1,3-diene (33) and pentacarbonyliron in two steps [74, 75]. Using catalytic amounts of a... 

Tricarbonyl(Ti -cyclohexadienylium)iron tetrafluoroborate was described first by Fischer in 1960. The required tricarbonyl(T -cyclohexadiene)iron complex can be conveniently obtained in high yield from cyclohexa-1,3-diene and pentacarbonyliron using catalytic amounts of a 1-azabuta-1,3-diene (see Section 2.5.1). Hydride abstraction from the tricarbonyl(ri -cyclohexadiene)iron complex using triphenylmethyl tetrafluoroborate affords the Ti -dienyliumiron complex salt almost quantitatively (Scheme 4-1... 

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