Pentadiene complexes with iron

Pentadentate 2,2 6, 2"-terpyridine, 30 107 Pentadiene complexes with iron, 12 255-257 with rhodium, 12 295 with silver, 12 340 Pentadienyl complexes with group VIB metals, 12 224, 225 with group VIIB metals, 12 240 JV,Af,/V,lV",N"-Pentaethyldiethylenetriamine, 42 76... 

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). 

X-ray studies have revealed a long iron-iron bond (3.14 A) in [ Fe(CO)a-(i -allyl) 2], in agreement with the ability of the dimer to dissociate into Fe(CX))3-(allyl) radicals. The complex slowly decomposes in solution to give ferracyclo-pentadiene complexes such as (25) via hydrogen abstraction and carbon-carbon coupling reactions. "... 

Reactions of diene-Fe(CO)3 complexes with other molecules capable of forming ligands with metals in low oxidation states can result in either displacement of the diene ligand or of one of the carbonyl groups. For example, the Fe(CO)3 complexes of with triphenylphosphine with liberation of the hydrocarbon ligands 34,19). Cyclooctatetraene-iron tricarbonyl gives cyclooctatetraene when treated with P 3 but with As 3 or Sb 3 the... 

Thus raM -l,3-pentadiene-Fe(CO)3 fails to react with the triphenyl-methyl fluoroborate under conditions favorable for hydride abstraction in the cyclic series. On the other hand ctf-l,3-pentadiene-iron tricarbonyl (LXXXV) reacts readily under the identical conditions to yield pentadienyl-iron tricarbonyl fluoroborate (LXXXVI) 32). The same cation is obtained from reaction with strong acids (37). Hydrolysis of the cation (LXXXVI) regenerates the alcohol complex while reduction with NaBH4 produces (LXXXV) this latter reaction constitutes the only means to date of making the ar-pentadiene complex (32). These reactions are given in Eq. 14. 

With the low-valence iron pentacarbonyl, vinylcyclopropanes 22 are thermally transformed to the diene re-complexes, the (1,3-trans-pentadiene)iron carbonyl complexes 23, through bond fission, 1,2-hydrogen shift, and stereoselective coordination [15]. (Scheme 9)... 

Nonconjugated dienes are rearranged to iron carbonyl complexes of conjugated dienes when treated with FefCOjs or Fe3(CO)i2. Thus 1,4-pentadiene gives tmw -l,3-pentadieneiron tricarbonyl (34) possibly by the route ... 

The vinylcyclopropanes (87) interact with Fe(CO)5 to give the complexes (mechanism involving complex formation at the vinyl double bond followed by opening of the cyclopropane ring to give a 7r-allylic intermediate with an iron-carbon a bond has been mentioned (513). 

As with the pentadienes, the complex formed with cyclopentadiene is dependent upon the iron carbonyl employed. 

Iron complexes favor the codimerization of BD with alkynes in a 1 1 ratio to (substituted) cyclohexadienes [39]. Two BD molecules and one alkyne give cyclodecatrienes with zerovalent nickel catalysts and good electron-donating ligands such as Ph3P [7, 40]. Ten-membered rings are in fact the principal products of such a reaction the variety of dienes seems to be limited to BD, iso-prene and 1,3-pentadiene, whereas numerous alkynes - simple alkyl-substituted alkynes, alkynes with aprotic functional groups, dialkynes, and cyclic alkynes... 

There exists a limitation to this direct method of synthesis in the case of acyclic dienes having m-alkyl substituents. Although these compounds may give rise to diene-Fe(CO)3 complexes, the ligand in the complex invariably involves a rearranged diene and, as of now, no m-substituted acyclic diene appears to have been prepared by the direct reaction. For example, 2,5-di-methyl-2,4-hexadiene (XVII) reacts with Fe(CO)5 to give trans-2,S-6x-methyl-l,3-hexadiene-iron tricarbonyl (XVIII) 41). Likewise, 4-methyl-1,3-pentadiene (XIX) gives ra r-2-methy 1-1,3-pentadiene-iron tricarbonyl... 

The reaction of malonate with the 3-methylpentadienyliron cation has been investigated in terms of regioselectivity. Strongly associated malonate salts lead to nucleophilic attack at Cl to give (ti -pentadiene)iron complexes. In case of dissociated malonate-counterion pairs, the reaction occurs at the C2 internal carbon atom of the... 

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