Iron complexes butadiene

Since such catalytic cycles involve transformations of organic species at a metal centre, a first step must be the formation of an organometallic. These can be formed by a direct reaction in which an organic reactant replaces a solvent or ligand molecule in the coordination sphere of a metal complex. For example, the ethylene-palladium(II) complex Pd(ri -C2H4)Cl2 2 can be formed by the direct reaction of PdCl2 with ethylene (Equation 1), and the butadiene-iron complex is also formed directly by replacement of two CO s on Fe (Equation 2). 

Dehydration of (2-hydroxymethyl-1,3-butadiene)iron complexes or (hydroxymethyltrimethylenemethane)iron complexes with fluorosulfonic acid/liquid sulfur dioxide generates the corresponding (cross-conjugated dienyljiron cations (194) (equation 72). The H and NMR spectral data for these cations favor an " -TMM-methyl cationic structure (282) over an ) " -isoprenyl cationic stmcture (283). These cations react with water or alcohols to afford butadiene products via nucleophilic attack at C-5. As indicated earlier (Section 6.1.1), the cross-conjugated dienyl cations are believed to be intermediates in the substitution of (193) with weak carbon nucleophiles (Scheme 53). In these cases, nucleophihc attack occurs on C-4 to give predominantly TMM products. ... 

Tricarbonyliron diene complexes have found many uses in synthetic chemistry but their synthesis is often not easy. Knolker has developed a range of tricarbonyl(7] -l-aza-l,3-butadiene) iron complexes that are excellent transfer agents for the Fe(CO)3 complexation of 1,3-dienes, and showed their versatility. As an extension to this work, Knolker and Gonser have prepared a polymer-supported l-aza-l,3-butadiene 321 by reaction of Merrifield s resin with phenolic l-aza-l,3-butadiene 320, formed from cinnamaldehyde and /> ra-hydroxyaniline (Scheme 105). The corresponding tricarbonyl iron complex 322 was formed by treatment of 321 with an excess of Fe2(CO)9 in THF using ultrasound. The iron complex was subsequently used efficiently as a transfer agent for the tricarbonyliron complexation of 1,3-dienes. 

Substituted cyclobutenes (225) are formed by the reaction of tricarbonylcyclo-butadiene iron complexes (226) with electrophiles. With a chiral complex (226a) the cyclobutenes formed are also chiral, and the inference is that the reaction must involve attack of electrophile on complexed cyclobutadiene rather than on free cyclobutadiene. In contrast, the cyclobutadiene Diels-Alder adducts (227) produced by oxidation of the optically active complexes in the presence of dieneophiles are racemic, indicating the intermediacy of the free cyclobutadienes. ... 

As shown in Scheme 15.8, if 1,3-butadiene iron complex is acylated, the diene is protected and the one terminal carbon is acylated. Further reaction with NaBH4 means the acyl group is selectively and quantitatively reduced to the hydroxy group while protecting the carbon-carbon double bond. The treatment with HPF6 yields a pale yellow cation. The nucleophilic substitution reaction of the 5-carbon of the cation is liable to proceed the nucleophile attacks the back side of the iron to produce the exo product as shown in Scheme 15.8 [82,83]. 

Scheme 4-104. Tricarbonyl(T -1 -aza-1,3-butadiene)iron complexes as tricarbonyliron transfer reagents.

Tricarbonyl(T -l-aza-l,3-butadiene)iron complexes constitute convenient tricarbonyliron transfer reagents, which are easier to handle than the corresponding T -benzylideneacetone(tricarbonyl)iron complexes. They are prepared from 1-aza-1,3-butadienes with nonacarbonyldiiron in tetrahydrofuran at room temperature. The... 

Scheme 4-105. Mechanism of the tricarbonyliron transfer by tricarbonyl(T -l-aza-l, 3-butadiene)iron complexes.

Methoxybutadiene has been complexed photochemically using Fe2(CO)9, instead of the more conventional thermal conditions. Complexation of acyclic dienes with Fe2(CO)9 constituted the first step toward trimethylenemethane complexes. All details concerning the preparation and spectral properties of tricarbonyl(butadiene)iron complexes are gathered in recent reviews. ... 

Other Reactions. Due to the highly reactive conjugated double bonds, butadiene can undergo many reactions with transition metals to form organometaHic complexes. For instance, iron pentacarbonyl reacts with butadiene to produce the tricarbonyl iron complex (10) (226). This and many other organometaHic complexes have been covered (227). 

Cycloaddition of 2-alkoxy-l,3-butadienes, H2C=C(OAlk)CH=CH2, and nitrile oxides to give isoxazolines 51 proceeds with the participation of only one of the conjugated C=C bonds. With benzonitrile oxide, only the vinyl group in alkoxydienes participates in cycloaddition reactions while in the case of phenyl-glyoxylonitrile oxide both double bonds react (222). Nitrile oxides RC=NO react with iron complexed trienes 52. The reaction proceeds with good yield and diastereoselectivity ( 90/10) to give isoxazolines 53 (223). 

However, upon thermolysis of 178.d or 178.h, isomeric mixtures of the butadiene complexes 183.a and 183.b were formed. Since intramolecular hydrogen transfer within (3,3-dime thyl-773 r -allylacy iron complexes is well precedented101 (see Section VI,B), it seems likely that this process is responsible for diene complex formation. Note that only the Z-diene complex was isolated from the reaction mixture, a surprisingly stereoselective result. 

The straight-chain 1- and 2-butenes can be converted into more butadiene when they are preheated in a furnace, mixed with steam as a diluent to minimize carbon formation, and passed through a reactor with a bed of iron oxide pellets. The material is cooled and purified by fractional distillation or extraction with solvents such as furfural, acetonitrile, dimethylformamide (DMF), and N-methylpyrrolidone (NMP). The conjugated n system of butadiene is attracted to these polar solvents more than the other C4 compounds. Extractive distillation is used, where the C4 compounds other than butadiene are distilled while the butadiene is complexed with the solvent. The solvent and butadiene pass from the bottom of the column and are then separated by distillation. 

C18H18, Benzene, l,3-butadiene-l,4-diyl-bis-cobalt complex, 26 195 C,8H33P, Phosphine, tricyclohexyl iron complex, 26 61 nickel complexes, 26 205, 206 C H 7OP, Benzenemethanol, 2-(diphenyl-phosphino)-... 

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... 

Selective osmylation of trienes.10 The (tricarbonyl)iron-complexed triene 2, prepared from the butadiene-tricarbonyliron 1 (11, 222), undergoes osmylation to give a single racemic, cij-diol 3 in 96% yield. Reaction of 3 with N,N -carbonyldi-nnidazole provides the single carbonate 4." Related carbonates, prepared from d-... 

Palladium-catalyzed methylene transfer from diazomethane has proved effective for the cyclopropanation of 1-alkenylboronic acid esters allylic alcohols and amines 1-oxy-l,3-butadienes and allenes " Readily accessible iron complex (CO)2FeCH2S Me2 BF4 35 undergoes direct reaction with a range of alkenes to give cyclopropanes (equation 67) The salt is sensitive to steric effects and the reaction proceeds... 

The crystal structure analysis (64) of the vitamin A aldehyde complex (75) (R = CHO), which confirms that suggested (63) on the basis of the NMR spectrum, shows a bonding of the Fe(CO)3 to the polyene chain quite analogous to that observed in several butadiene-(or substituted butadiene-)metal complexes (59, 113). The iron-carbon atom distances and the carbon-carbon bond lengths, clearly suggest (64) a CT,7r-bonded rather than a two-rr-bonded structure. A similar a,Tr bonding has been proposed for the complexes l,l -bicyclopentenyl, -hexenyl, and -heptenyltricarbonyliron (76) (391), and for the tricarbonyliron complex... 

Even though the X-ray data suggest the presence of two a bonds and one 7T bond between metal and olefin as was postulated for the butadiene-iron carbonyls, the UV spectra of the triphenyltropone complexes closely resemble that of the free olefin (80) suggesting that the bonding of the complex may indeed be intermediate between that of structure (96) and simple rr bonding to two olefinic double bonds (80). This concept is more fully discussed in the section on cobalt (Section VII, A). 

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). 

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