Iron‐Mediated Coupling of Two Ethyl Anions to Form a 2‐Butyne Ligand

Abstract

The σ‐aryliron complexes [5CpFe(C6H3iPr2‐2,6)] (2, 5Cp = η5‐C5iPr5) and [4CpFe(C6H3iPr2‐2,6)] (6, 4Cp = η5‐C5HiPr4) are available from the halides [5CpFe(μ‐Br)]2 (1) and [4CpFe(μ‐Br)]2 (4) and have been used for σ/π rearrangement reactions with trialkylaluminum compounds. Whereas trimethylaluminum can be added to 2 and 6 to form the aryltrimethylaluminate complexes [5CpFe(μ,η6:η1‐C6H3iPr2‐2,6)AlMe3] (3) and [4CpFe(μ,η6:η1‐C6H3iPr2‐2,6)AlMe3] (7) in clean σ/π rearrangement reactions, the addition of tripropylaluminum to 6 afforded a mixture containing the aryl(bromo)dipropylaluminate complex [4CpFe(μ,η6:η1‐C6H3iPr2‐2,6)AlBr(C3H7)2] (8). With triethylaluminum, a similar product mixture was obtained and could be separated to yield the aryl(bromo)diethylaluminate [4CpFe(μ,η6:η1‐C6H3iPr2‐2,6) AlBr(C2H5)2] (9), the aryltriethylaluminate [4CpFe(μ,η6:η1‐C6H3iPr2‐2,6)Al(C2H5)3] (10), the arene complex [4CpFe(η6‐C6H4iPr2‐1,3)]Br (11), and the 2‐butyne complex [(4CpFe)2(μ,η2:η2‐MeCCMe)] (12). The formation of 12 involves the coupling of two ethyl groups with the loss of four hydrogen atoms and could also be observed in reactions of the bromide dimer 4 or the σ aryl complex 6 with ethylmagnesium bromide. The aluminates 3, 7, 8, and 10, the arene sandwich 11, the 2‐butyne complex 12, as well as the alkylcyclopentadienyliron(II) halides [5CpFe(μ‐Br)]2 (1), [4CpFe(μ‐Br)]2 (4), and [4CpFe(μ‐I)]2 (5) have been crystallographically characterized.

Paramagnetic Chromium(II) Complexes and Chromium(IV) Nitrides with Bulky Alkylcyclopentadienyl Ligands

“…Bulky alkylcyclopentadienyl ligands have been seen in a small number of chromocenes, and in one mono(cyclopentadienyl)chromium complex [Cp′′′Cr(µ‐Cl)] 2 . Chromium(II) half sandwich complexes without π acceptor ligands promise to be even more reactive than the nickel, or iron precedents studied before: The 94 pm radius of chromium(II) ions in their high spin state is surpassed among the M 2+ cations of the 3d row only by Ti 2+ and opens Cr II half sandwich complexes for chemical reactions. Such complexes should be strongly reducing, because chromium(III) with its d 3 configuration is the most stable oxidation state.…”

Iron(III) Half‐Sandwich Complexes of the Two‐Legged Piano‐Stool [CpFe(aryl)Cl] Type from the Corresponding Aryliron(II) Precursors

“…The mesityl ligands of 2 are oriented such that one methyl group in an ortho position lies underneath the substitution gap of the cyclopentadienyl ligand, and the other is underneath the two adjacent isopropyl substituents pointing away from each other. With a deviation of 4.8–5.4° from the ideal 180° angle between the Cp centroids and the ipso ‐carbon atom, complex 2 can be considered to have a structure similar to an umbrella, comparable to those of other (σ‐aryl)(cyclopentadienyl)iron(II) complexes such as 1 , [ 4 CpFe(σ‐C 6 H 3 i Pr 2 ‐2,6)], and [ 5 CpFe(σ‐C 6 H 3 i Pr 2 ‐2,6)] ( 5 Cp = pentaisopropylcyclopentadienyl) …”

“…The crystal structures were obtained by XRD measurements with a Stoe IPDS diffractometer (5) or an Oxford Diffraction Gemini Ultra diffractometer (others). The mass spectra were recorded with a [9] [ 5 CpFeBr(dme)] (dme = 1,2-dimethoxyethane), [10] mesitylmagnesium bromide, [16] mesityl(tri-tert-butylcyclopentadienyl)iron (1), [6] (2,6-diisopropylphenyl)magnesium bromide, [10] (2,6-diisopropylphenyl)(tetraisopropylcyclopentadienyl)iron (3), [8] and (2,6-diisopropylphenyl)-(pentaisopropylcyclopentadienyl)iron (4) [10] were synthesized according to literature procedures. Hexachloroethane (Acros, 99 %) was used as purchased.…”

“…Four paramagnetic (alkylcyclopentadienyl)(aryl)iron(II) complexes used as starting compounds: [Cp′′′Fe(σ-C 6 H 2 Me 3 -2,4,6)] (1), [6] [ 4 CpFe-(σ-C 6 H 2 Me 3 -2,4,6)] (2; this work), [ 4 CpFe(σ-C 6 H 3 iPr 2 -2,6)] (3), [9] [ 5 CpFe-(σ-C 6 H 3 iPr 2 -2,6)] (4). [10] As the σ-aryl complex 2 has not been described previously, we report its synthesis and discuss its molecular structure before we proceed to the oxidation of these iron(II) compounds.…”

“…Four paramagnetic (alkylcyclopentadienyl)(aryl)iron(II) complexes used as starting compounds: [Cp′′′Fe(σ‐C 6 H 2 Me 3 ‐2,4,6)] ( 1 ), [ 4 CpFe(σ‐C 6 H 2 Me 3 ‐2,4,6)] ( 2 ; this work), [ 4 CpFe(σ‐C 6 H 3 i Pr 2 ‐2,6)] ( 3 ), [ 5 CpFe(σ‐C 6 H 3 i Pr 2 ‐2,6)] ( 4 ) …”