Abstracts Chemistry

Radical Reactions of Acyclic Butadienyliron and Cyclohexadienyliron Tricarbonyl Complexes

by Ming Z. Chen

Density functional calculations in combination with isodesmic reactions indicated that acyclic butadienyliron and cyclohexadienyliron tricarbonyl radicals were 13.7 and 16.3 kcal/mole more stable than benzylic radical, respectively. This exceptional stability was a result of substantial spin delocalization onto the iron atom. The thiocarbonyl diimidazole (TCDI) derivatives of the two complexes were used as the radical precursors. These two radicals were found to be too stable to propagate radical chain reactions with Bu3SnH. Their nucleophilicity was demonstrated by trapping them with electron-deficient alkene, namely 2-carboethoxyallyltributylstannane. The alkylated product of acyclic butadienyliron tricarbonyl radical could not be fully characterized since complete removal of the chromatographically "streaky†tin byproducts was not successful. Cyclohexadienyliron tricarbonyl radical was found to be unreactive with the alkene. Addition of tert-butyl radical to tricarbonyl(1-methylpentadienyl)iron (I) cation gave rise to a minor alkylated product as evidenced by GC/MS, while addition to tricarbonyl(cyclohexadienyl)iron (I) cation gave rise to the desired product in greater than 50% yield. One-electron reduction of tricarbonyl (1-methylpentadienyl)iron (I) cation by zinc followed by nucleophilic addition to 2-carboethoxyallyltributylstannane gave rise to a dimerization product rather than the expected alkylated product.