Iron, tricarbonyl reactions with carbanions

Anionic (77 -allyl)iron tricarbonyl complexes are easily prepared by the hydride reduction of (butadiene)iron tricarbonyl or (l-phenylbutadiene)iron tricarbonyl complexes with Li[BHEt3] in THF. Tricarbonyl(r7" -l,3-diene)-iron(O) complexes undergo addition reactions with reactive carbanions, such as LiCHPh2, to form anionic tricarbonyl(77 7 -but-3-en-l-yl)iron(0) complexes. 

Dienes form very stable complexes with a variety of metal caibonyls, particularly Fe(CO)s, and the neutral V-diene metal carbonyl complexes are quite resistant to normal reactions of dienes (e.g. hydrogenation, Diels-Alder). However, they are subject to nucleophilic attack by a variety of nonstabilized carbanions. Treatment of -cyclohexadiene iron tricarbonyl with nonstabilized carbanions, followed by protonolysis of the resulting complex, produced isomeric mixtures of alkylated cyclohexenes (Scheme 15).24 With acyclic dienes, this alkylation was shown to be reversible, with kinetic alkylation occurring at an internal position of the complexed dienes but rearranging to the terminal position under thermodynamic conditions (Scheme 16).2S By trapping the kinetic product with an electrophile, overall carbo-... 

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