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

The σ‐aryliron complexes [ 5 CpFe(C 6 H 3 i Pr 2 ‐2,6)] ( 2 , 5 Cp = η 5 ‐C 5 i Pr 5 ) and [ 4 CpFe(C 6 H 3 i Pr 2 ‐2,6)] ( 6 , 4 Cp = η 5 ‐C 5 H i Pr 4 ) are available from the halides [ 5 CpFe(μ‐Br)] 2 ( 1 ) and [ 4 CpFe(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 [ 5 CpFe(μ,η 6 :η 1 ‐C 6 H 3 i Pr 2 ‐2,6)AlMe 3 ] ( 3 ) and [ 4 CpFe(μ,η 6 :η 1 ‐C 6 H 3 i Pr 2 ‐2,6)AlMe 3 ] ( 7 ) in clean σ/π rearrangement reactions, the addition of tripropylaluminum to 6 afforded a mixture containing the aryl(bromo)dipropylaluminate complex [ 4 CpFe(μ,η 6 :η 1 ‐C 6 H 3 i Pr 2 ‐2,6)AlBr(C 3 H 7 ) 2 ] ( 8 ). With triethylaluminum, a similar product mixture was obtained and could be separated to yield the aryl(bromo)diethylaluminate [ 4 CpFe(μ,η 6 :η 1 ‐C 6 H 3 i Pr 2 ‐2,6) AlBr(C 2 H 5 ) 2 ] ( 9 ), the aryltriethylaluminate [ 4 CpFe(μ,η 6 :η 1 ‐C 6 H 3 i Pr 2 ‐2,6)Al(C 2 H 5 ) 3 ] ( 10 ), the arene complex [ 4 CpFe(η 6 ‐C 6 H 4 i Pr 2 ‐1,3)]Br ( 11 ), and the 2‐butyne complex [( 4 CpFe) 2 (μ,η 2 :η 2 ‐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 [ 5 CpFe(μ‐Br)] 2 ( 1 ), [ 4 CpFe(μ‐Br)] 2 ( 4 ), and [ 4 CpFe(μ‐I)] 2 ( 5 ) have been crystallographically characterized.