Organoiron complexes in organic synthesis
Several (1-substituted-pentadienyl)iron(+1) complexes were synthesized (II-8a R = Me, II-8b R = Et, II-8c R = Pr, II-8d R = Bu, II-8e R = pentyl, II-8f R = hexyl, II-8g R = heptyl, II-8j R = Ph, II-8k R = COOMe, and II-8l R = COOEt). The reaction of II-8a, II-8b, II-8c, II-8j, II-8k, and II-8l was investigated. The reaction of II-8a, II-8b, II-8c, and II-8j gave (diene)iron compounds due to attack at the dienyl terminal carbons. Depending on the nature of the substituent, either cis(diene)iron and/or cis,trans(diene)iron products were obtained. The ratio of these regiomers depends on the nature of the substituent on the cation. (1-alkyl-pentadienyl)iron(+1) cations, II-8a ... II-8c gave a mixture of cis(diene)iron and cis,trans(diene)iron and cis,trans(diene)iron complexes. (1-phenyl-pentadienyl)iron(+1) cation gave cis(diene)iron products. It appears that the nucleophilic attack to II-8a, II-8b, II-8c and II-8j is under overall frontier orbital control. Surprisingly when (pentadienyl)iron(+1) cation II-8k and II-8l were reacted with lithio dimethylmalonate gave $\pi$-$\sigma$-allyl complexes III-68, and III-69 respectively from nucleophilic attack at the internal dienyl carbon (C2) due to charge control. Decomplexation of III-68 and III-69 with Ce(NH$\sb4)\sb2$(NO$\sb3)\sb6$ gave trisubstituted cyclopropane carboxylates III-77 and III-78 respectively. Unlike the malonate anion, the reaction of lithio phenylacetylene with the cations II-8a and II-8k gave only decomposed products. The reaction of dilithio -tris(phenylethynyl)cuprate and dilithio tris(heptynyl)cuprate with (pentadienyl)iron(+1) cations, II-8a, II-8j and II-8k gave only (E,Z-dienyne)iron complexes (III-80, III-81, III-82, and III-83) due to attack at the unsubstituted dienyl terminal carbon. The alkynylcuprates addition to (pentadienyl)iron(+1) cations is under overall frontier orbital control. The reaction of trimethylsilylphenylacetylene and trimethylsilylheptyne with (1-methoxycarbonyl-pentadienyl) cation, II-8k gave only (E,E-dienyne)iron complexes (III-84 and III-85) respectively.
"Organoiron complexes in organic synthesis"
(January 1, 1989).
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