Design of 2D nanocrystals

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.

Metal−metal cooperativity in action! Different fragments are combined on the {Fe₂Cp₂(CO)₂} skeleton to give highly functionalized selenophene ligands, linked to the iron centers through a bridging alkylidene, which is easily removed from coordination by exposure to air/water in ethereal solution.