Ferrocenes Containing a Pendant Propargylic Chain Obtained via Addition of Propargyl Alcohol to μ-Vinyliminium Ligands in Diiron Complexes

The diiron bridging vinyliminium complexes [Fe₂{μ-η¹:η³-CN­(Me)₂C­(R′)C­(R″)}­(μ-CO)­(CO)­(Cp)₂]­[SO₃CF₃] (R′ = H, R″ = SiMe₃, <b>3a</b>; R′ = H, R″ = Tol =4-MeC₆H₄, <b>3b</b>; R′ = Me, R″ = Me, <b>3c</b>; R′ = SPh, R″ = Me, <b>3d</b>; R′ = H, R″ = Fc = [Fe­(C₅H₄)­(Cp)], <b>6e</b>) react with propargyl alcohol (HCCCH₂OH), in refluxing toluene, affording the polysubstituted ferrocenes as mixtures of two isomeric forms: [1-NMe₂-2-R′-3-R″-5-CH₂OCH₂CCH-Fc] (R′ = H, R″ = SiMe₃, <b>6a</b>; R′ = H, R″ = Tol, <b>6b</b>; R′ = Me, R″ = Me, <b>6c</b>; R′ = SPh, R″ = Me, <b>6d</b>, R′ = H, R″ = Fc, <b>6e</b>) and [1-NMe₂-2-R′-3-R″-4-CH₂OCH₂CCH-Fc] (R′ = H, R″ = SiMe₃, <b>7a</b>; R′ = H, R″ = Tol, <b>7b</b>; R′ = Me, R″ = Me, <b>7c</b>; R′ = SPh, R″ = Me, <b>7d</b>) in overall yields of about 55–65%. Formation of the functionalized cyclopentadienyl in the ferrocene products takes place through the assembly of two propargyl units with the bridging vinyliminium ligand: one alkynol is incorporated by a [3 + 2] cycloaddition with the bridging C₃ ligand; a second alkynol unit gives rise to a pendant chain through −OH substitution. Investigations show that the substitution step is catalyzed by the parent diiron complex itself or by a mononuclear iron fragment (likely the Fp⁺ complex). The pendant propargyl chain has been exploited to connect the ferrocene to other molecular fragments: in particular, the reaction of <b>6a</b> with 4-biphenyl azide, by copper-catalyzed azide–alkyne cycloaddition (CuAAC), leads to the formation of the triazole-functionalized ferrocene [1-NMe₂-2-CH₂OCH₂-N₃(C₆H₄Ph)­C₂H-4-SiMe₃-Fc] (<b>12</b>). Moreover, <b>6a</b> reacts with Co₂(CO)₈, affording the complex [Co₂{μ-η²-HCCR}­(CO)₆] (<b>13</b>), (HCCR = <b>6a</b>), where the alkyne adopts a η² coordination to a dicobalt hexacarbonyl fragment. The molecular structure of <b>7a</b> has been determined by X-ray diffraction studies