Iron tricarbonyl, 1,3-butadiene complex

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. 

Haas and Wilson (117) have studied a number of substituted butadiene-iron tricarbonyl complexes, finding that in most cases loss of three CO groups precedes fragmentation of the ligand. Compared with the ligands the spectra of the complexes show a number of instances where the iron atom tends to stabilize odd-electron ions. In (XV), the presence of the ion... 

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. 

The binuclear iron complex (C8H8)Fe2(CO)6 had been expected from the reaction, but the chair conformation (XXXV), which was subsequently found for this substance, was entirely unexpected (65j 66j 67). In this complex, each end of the cyclooctatetraene ligand behaves as a butadiene-type (n = 4) ligand, and bond distance measurements indicate very little tt-tt interaction between the two halves of the ring. The proton NMR spectrum of the complex in solution exhibits two resonances of equal intensity, while the infrared spectrum is very similar to the spectrum of butadiene-iron tricarbonyl and similar diene complexes (105). 

Cyclobutadiene-iron tricarbonyl is prepared through reaction of S,4-dichlorocydolmtene and diiron enneacarbonyl. In an analogous manner, one can prepare 1,2-diphenyl- 1,2,3,4-tetramethyl- and benzocyclobutadiene-iron tri-carbonyl complexes. Cyclobutadiene-iron tricarbonyl is aromatic" in the sense that it undergoes facile attack by electrophilic reagents to produce monosubstituted cydo-butadiene-iron tricarbonyl complexes. Functional groups in the substituents display many of their normal chemical reactions which can be used to prepare further types of substituted cyclobutadiene-iron tricarbonyl complexes. 

Chiral electrophilic cyclopropanes (63) are prepared in high enantiomeric excess starting from butadiene-iron tricarbonyl complexes (60) containing a non-complexed double bond. Reaction with diazomethane and decomposition of the resulting pyrazolines (61) in the presence of Ce" gave the corresponding chiral cyclopropanes (62). Breakdown of the dienic substituent of electrophilic cyclopropane (62) by means of ozonization resulted in the formation of formyl-substituted electrophilic cyclopropane (63) still carrying the asymmetric centre (equation 10) " . ... 

Chiral eyelopropanes. Carrie et al.6-1 have developed a highly enantioselective synthesis of cyclopropanes from the aldehyde 2, in which the butadiene group is protected as the iron tricarbonyl complex. The complex (2) is resolved by the method of Kelly and Van Rheenan (5, 289-290), and the two optical isomers are then converted separately into a cyclopropanealdehyde (5a and 5b) as formulated. A sulfur ylide such as (CH3)2S=CHCOOCH3 can be used in place of diazomethane for cyclopropanation. Optical yields are >90%. 

Malthete has reported some five-coordinate butadiene iron tricarbonyl complexes (Figure 61) exhibiting a wide range of nematic phase for type A, and nematic, Sa or... 

The low lying ji -orbitals of conjugated dienes explain the stability of many diene metal carbonyl complexes e.g. butadiene iron tricarbonyl 382>. Photochemical preparation of the latter 286> is superior to the thermal procedure 272>. Mercury can be used as a sensitizer in the photoreaction of metal carbonyls with dienes I09.i7o,i76,24i)... 

The catalytic dimerization at 100 °C of butadiene (and isoprene) with dicarbonyldinitrosyliron and dicarbonylnitrosyl( r-allyl)iron [1—2 wt. %] to 4-vinylcyclohex-l-ene (CHs-substituted vinylcyclohexenes) can be carried out photochemically at —10 °C to 25 °C. It has been suggested, that intermediates formed by UV decomposition of the complexes may be the active catalysts, and that these intermediates could be the same as those produced thermally. u-Allyl iron tricarbonyl iodide was found to be ineffective as a thermal dimerization catalyst 90>. However, u-methallyl iron tricarbonyl bromide has been shown to be effective in the trimerization of isobutylene 284> [see section G2a],... 

Although few examples of acylations of 1,3-butadienes have been described, Friedel-Crafts acylations of diene complexes, in particular iron tricarbonyl derivatives, can give synthetically useful yields. In acylations of iron tricarbonyl complexes with the Perrier reagent from acetyl chloride and aluminum chloride, acylation occurs only at unsubstituted terminal carbons (Scheme 18). ° The primary product is... 

By analogy with the behaviour of the iron tricarbonyl complex of benzocyclo-butadiene, formation of ferrole (158) from cyclododeca-l,7-diyne and iron penta-... 

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