Comparison of the oxidation of dinuclear cyclopentadienyl iron diphosphine complexes with the bridging ligands -CN and -C≡C(CH2)2CN

Article abstract of DOI:10.1016/0022-328X(95)05829-E

The alkynyliron complex [Fe(C≡C-CH₂CH₂-CN)(dppe)(C₅H₅)] (2) (dppe = Ph₂PCH₂CH₂PPh₂), prepared from [Fe(C≡C-CH₂CH₂-CN)(CO)₂(C₅H₅)] (1) and dppe under UV irradiation, reacted with HBF₄ Et₂O in tetrahydrofuran and with NH₄[PF₆] in CH₂Cl₂ to give the cationic vinylidene derivative [Fe(=C=CH-CH₂CH₂-CN)(dppe)(C₅H₅)][A] (A = BF₄ (3a) or PF₆ (3b)), which can be reconverted to 2 with K₂CO₃ in CH₂Cl₂. The compound [(C₅H₅)(dppe)Fe-NC-CH₂CH₂-C≡CH][PF₆] (4), which is a tautomeric form of 3 was prepared by reaction of [Fe(I)(dppe)(C₅H₅)] with the alkyne HC≡C-CH₂CH₂CN in the presence of NH₄[PF₆] in CH₂Cl₂. The dinuclear compound [(C₅H₅)(dppe)Fe-C≡C-CH₂CH₂-CN-Fe(dppe)(C₅H₅)][PF₆] (5), which is unstable, can be formed by reaction of 2 with [Fe(NCMe)(dppe)(C₅H₅)] PF₆ in CH₂Cl₂. Its electrochemical oxidation shows that there is no electronic interaction between the two metal centres. Extended Hckel molecular orbital calculations have been carried out on the model complexes [(C₅H₅)(PH₃)₂Fe-C≡C-CH₂CH₂-CN-Fe(PH₃)₂(C₅H₅)]⁺ (7) and [(C₅H₅)(PH₃)₂Fe-CN-Fe(PH₃)₂(C₅H₅)]⁺ (8).