Allyl cations, iron carbonyl complexes

The reaction between the allylic bromide (37) and Fe(CO)s constitutes an alternative method of preparation of tricarbony 1( 1,3-cyclohexadiene)iron (38) (eq 16). Allylic alcohols react in a similar way (eq 17) under neutral conditions, but in the presence of acid (HBF4), cationic iron carbonyl complexes are produced. ... 

Iron carbonyl complexes containing 77 -alkyl-77 -allyl coordinated hydrocarbon ligands are obtained in several ways. Nucleophilic addition to cationic iron complexes containing 77 -pentadienyl ligands yields (pentenediyl)iron complexes. Oxidatively-induced reductive elimination of these complexes can be utilized as a means to generate 1,2,3-trisubstituted cyclopropanes.The reaction of cationic cycloheptadienyl complexes (Scheme 22) with appropriate nucleophiles also yields the alkyl-allyliron carbonyl complexes. Fe(CO)s also reacts with a- or /3-pincnc in refluxing dioxane (Scheme 22) to produce an alkyl-allyliron complex. Recently, 1,2- and 1,4-disubstituted [(pentadienyl)Fe(CO)3] cations were shown to react with carbon nucleophiles, such as sodium dimethylmalonate, to yield 77 77 -allyl complexes as products. 

The reactions of various iron carbonyl complexes, such as Fe(GO)4(NMe3), with allene compounds under photo-lytic conditions, yield chelated 77 -allyliron complexes. Two brief reviews discussing the chemistry and application to organic synthesis of these (7r-allyl)tricarbonyl iron lactone complexes have appeared recently. Reaction of the iron lactone complexes with trimethyloxonium tetrafluoroborate yields the carbene complex 23 in good yields. Treatment of the cationic carbene complex with triphenylphosphine results in substitution at the terminal end of the allyl ligand of the trimethylenemethane complex 24. 

Since 1958 a considerable amount of research activity has centered around these systems, both in the acetylene-iron carbonyl reactions and the direct reactions of olefins with iron carbonyls. The types of unsaturated ligands which are now known to occur in stable iron carbonyl complexes include substituted and nonsubstituted cyclic, acyclic, and nonconjugated dienes as well as some aromatic systems. Furthermore, what may be formally regarded as dienyl cations as well as allyl cations and radicals are found to... 

Iron complexes can also catalyze allylic amination [31,32]. Enders et al. have demonstrated the nucleophilic addition of various acyclic and cyclic amines to the optically active l-methoxycarbonyl-3-methyl-(T)3-allyl)-tetracarbonyliron cation 49 formed in high yield from reaction of 48 with iron carbonyls. Oxidative removal of the tetracarbonyliron group by reaction with CAN gives 50 with high optical purity and retention of the stereochemistry (Eq. (12)) [31]. The reaction proceeds well for the different amines, and has been used for the synthesis of a compound showing cytotoxic activity against diverse cell lines [31b]. 

Complexes M(CH2C CC=CMe)(CO)nCp [325 M = Mo, n = 3 M = Fe, = 2 (Scheme 74)] were obtained from the carbonyl anions and l-chlorohexa-2,4-diyne. Subsequent chemistry involves protonation (HBF4) to cationic allene or diene complexes, or addition of MeOH to give allylic derivatives, which are formed with concomitant insertion of CO. The latter can also be obtained from the cationic species and NaOMe. The allene-iron cation reacts with NHEt2 to form an ynenyl complex. The luminescent complex Re(CO)3(5,5 -Bu 2-bpy) 2 (At-C=CC6H4C CC=CC6H4C=C) has been reported. ... 

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