COMPARISON OF THE OXIDATION OF DINUCLEAR CYCLOPENTADIENYL IRON DIPHOSPHINE COMPLEXES WITH THE BRIDGING LIGANDS -CN AND -C-C(CH2)(2)CN

The alkynyliron complex [Fe(C=C-CH2CH2-CN)(dppe)(C5H5)] (2) (dppe = Ph (2)PCH(2)CH(2)PPh(2)), prepared from [Fe(C=C-CH2CH2-CN)(CO)(2)(C5H5)] (1) and dppe under UV irradiation, reacted with HBF(4)Et(2)O in tetrah ydrofuran 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 (3 b)), 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 o f 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 compo und [(C5H5)(dppe)Fe-C=C-CH2CH2-CN-Fe(dppe)(C5H5)][PF6] (5), which is u nstable, can be formed by reaction of 2 with [Fe(NCMe)(dppe)(C5H5)] PF (6)in CH2Cl2. Its electrochemical oxidation shows that there is no ele ctronic interaction between the two metal centres. Extended Huckel mol ecular orbital calculations have been carried out on the model complex es C5H5)(PH3)(2)Fe-C=C-CH2CH2-CN-Fe(PH3)(2)(C5H5)](+) (7) and [(C5H5)( PH3)(2)Fe-CN-Fe(PH3)(2)(C5H5)](+) (8).