Butadiene-tricarbonyliron

Borohydrides normally do not attack carbon-carbon multiple bonds, and thus, a, 3-unsaturated imines (1-aza-1,3-butadienes) are reduced only at their C=N bond, under both thermal and microwave conditions. However, the corresponding (1-aza-1,3-butadiene)tricarbonyliron(O) complexes show a totally different reactivity under the same conditions, and a simultaneous reduction of both C=N and C=C takes place if microwave irradiation is applied25. When the reaction was performed with sodium borodeuterid, 1,2,3-trideutero, secondary amines were obtained. In contrast to their behaviour under microwave conditions, these complexes were totally inert to reduction by NaBH4 under thermal conditions (Scheme 4.7)25. 

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-... 

Structural characterization of (butadiene)tricarbonyliron complexes has been carried out by microwave spectro-scopy/" " solution calorimetry/" pulsed-electron high pressure mass spectrometry/ infrared spectro-scopy/ and vibrational overtone spectroscopy/ Theoretical investigations using DFT have also been reported/ " Extended Hiickel calculations have been employed to study structure and stereodynamic relationships in a variety of ( 7" -diene)iron carbonyl complexes/ ... 

A short time after the first synthesis of a trimethylenemethane complex, Noyori et al. reported a new access to the class of compounds starting from methylenecyclopropane derivatives. While treatment of methylenecyclopropane with diironenneacarbonyl afforded 3 only in very poor yield in addition to (l,3-butadiene)tricarbonyliron, substituted systems such as 2-methyl-2-phenylmethylenecyclopropane (4) gave trimethylenemethane complexes such as 5 in up to 60% yield (Scheme 10.2) [14]. These results reflect the tendency of strained small rings to undergo ring-opening reactions in the presence of transition metal complexes. However, few stable complexes of methylenecyclopropane have been described [15]. 

Friedel-Crafts acylation of (butadiene)tricarbonyliron gives cis- and trans-(dienone)tricarbonyliron complexes via an isolable ionic intermediate (10), as shown in Scheme 3. Although (butadiene)tricarbonyliron is 3800 times as... 

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... 

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... 

The diene ligands transform to the cisoid form because of the thermodynamic stability of the complex. Because the bond distances of Cj—and C2—Cy in the butadiene ligand are 1.45 and 1.46 A, respectively, the double bond character between C2—C3 and the bond order alternation is still insignificant [43]. This may be due to the strong K-acidity of three carbonyl ligands which reduces n-back donation from iron to the butadiene ligand. (Cyclohexadiene)tricarbonyliron complexes are also noteworthy. Fe(l,3-cyclo-hexadiene)(CO)3 was prepared by the reaction of 1,3-cyclohexadiene with Fe(CO)5 [44] (eq (13)) and more stable Fe(l,4-cyclohexadiene)(CO)3 was also prepared [45]. 

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. 

Relatively little work has been done with simple coordinated dienes and electrophilic reagents in organic synthesis. Butadiene, as its tricarbonyliron derivative, undergoes Friedel-Crafts acylation much more readily than does benzene 2 3800). The product arises from attack by the acyl cation on the same side of the molecule as the iron atom [Eq. (60) (Greaves e/ ai, 1969, 1974 Graf and Lillya, 1972)] and at an outer position only. 

Silyl-substituted allyl acetates react with Fc2(CO)9 under a CO atmosphere to give the corresponding ij -Fe(CO)4 complexes which are treated with a silyl enol ether in the presence of BF3 OEt2 to yield vinylsilanes 245 stereoselectively in moderate to good yields (equation 198). Allylstannane can also react undo- these conditions. The silyl-substituted butadiene complex of tricarbonyliron is treated with acetyl chloride in the presence of AICI3 at 0°C to give the Friedel-Crafts acylation products, dienone complexes, without desilylation -. ... 

Ci3Hi FeO, Butadiene(cyclooctatetraene)iron monocarbonyl, 38B, 766 C13H1ftFeOs f (exo-2-Methoxy-5,6-dimethylene-syn-7-norbornanol)-endo-tricarbonyliron, 45B, 913... 

Tricarbonyliron lactone complexes have also been used as precursors for /3-lactam preparation. Reaction of the complex (9), which is readily available from butadiene, with a protected amino-acid leads to a new lactam complex, which on oxidation gives a /3-lactam related to the nocardicins (Scheme 29). ... 

Ghiral 1-aza-l,3-butadienes react with nonacarbonyldiiron in THF at RT using ultrasound, to yield a 5 1 mixture of the (S,R)-32 and R,R)-33 diastereoisomers, respectively. The crystal structure of 32 has been reported (Scheme 27). The free ligands of 1-aza-l,3-dienes are reported to be efficient catalysts for the complexation of 1,3-dienes with either pentacarbonyliron or nonacarbonyldiiron.In this respect, the heterodiene complexes serve as useful tricarbonyliron transfer reagents, to yield free 1-azabuta-1,3-dienes (Scheme 28). 

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.

The imino function adjacent to (diene)iron complexes can be employed in a hetero-Diels-Alder reaction with l-methoxy-3-trimethylsilyloxy-1,3-butadiene. This leads to tetrahydropyridinones pendent to the (diene)iron system. The biologically active piperidine alkaloid SS20846 A has been synthesized using this procedure. Ketones adjacent to the tricarbonyl(diene)iron unit can be reacted with nucleophiles using the stereodirecting effect of the tricarbonyliron moiety. Spiroketals are formed in good diastereoselectivity from appropriately functionalized 1- and 2-sulfinyl l,3-dien-5-ones under the stereodirecting influence of the tricarbonyliron moiety (Scheme 4-139). ... 

Two main classes of T -dienyliron complexes are known, namely the cationic tricarbonyliron complexes and neutral cyclopentadienyliron compounds. The cyclopentadienyl (Cp) ligand is relatively inert to a broad variety of reaction conditions. It is often introduced as a ligand to tune the properties of the iron complex, as a chiral auxiliary,or in material science in organoiron pol5miers. However, it is only rarely transformed itself into a more elaborate organic product. For this reason, the chemistry of the cyclopentadienyl ligand will not be discussed in more detail in this chapter. Tricarbonyl( n -dienylium)iron complexes, on the other hand, represent versatile electrophilic building blocks for the attachment of 1,3-butadiene, cyclohexadiene, or aromatic moieties to nucleophilic molecules. 

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