Tetrasubstituted Selenophenes from the Stepwise Assembly of Molecular Fragments on a Diiron Frame and Final Cleavage of a Bridging Alkylidene

A series
of 2,3-di­carboxy­lato-5-acetyl-4-amino­seleno­phenes, 5a–j, was obtained via the uncommon assembly
of building blocks on a diiron platform, starting from commercial
[Fe2Cp2(CO)4] through the stepwise
formation of diiron complexes [2a–d]­CF3SO3, 3a–d, and 4a–j. The selenophene-substituted
bridging alkylidene ligand in 4a–j is removed from coordination upon treatment with water in air under
mild conditions (ambient temperature in most cases), affording 5a–j in good to excellent yields. This
process is highly selective and is accompanied by the disruption of
the organometallic scaffold: cyclopentadiene (CpH) and lepidocrocite
(γ-FeO­(OH)) were identified by NMR and Raman analyses at the
end of one representative reaction. The straightforward cleavage of
the linkage between a bridging Fischer alkylidene and two (or more)
metal centers, as observed here, is an unprecedented reaction in organometallic
chemistry: in the present case, the carbene function is converted
to a ketone which is incorporated into the organic product. DFT calculations
and electrochemical experiments were carried out to give insight into
the release of the selenophene-alkylidene ligand. Compounds 5a–j were fully characterized by elemental
analysis, mass spectrometry, IR, and multinuclear NMR spectroscopy
and by X-ray diffraction and cyclic voltammetry in one case.