Olefin–aminocarbyne coupling in diiron complexes: Synthesis of new bridging aminoallylidene complexes

Abstract

The bridging aminocarbyne complexes [Fe 2{μ-CN(Me)(R)}(μ-CO)(CO) 2(Cp) 2][SO 3CF 3] (R = Me, 1a; Xyl, 1b; 4-C 6H 4OMe, 1c; Xyl = 2,6-Me 2C 6 H 3) react with acrylonitrile or methyl acrylate, in the presence of Me 3NO and NaH, to give the corresponding μ-allylidene complexes [Fe 2{μ-η 1:η 3- C α (N(Me)(R))C β (H)C γ (H)(R′)}(μ-CO)(CO)(Cp) 2] (R = Me, R′ = CN, 3a; R = Xyl, R′ = CN, 3b; R = 4-C 6H 4OMe, R′ = CN, 3c; R = Me, R′ = CO 2Me, 3d; R = 4-C 6H 4OMe, R′ = CO 2Me, 3e). Likewise, 1a reacts with styrene or diethyl maleate, under the same reaction conditions, affording the complexes [Fe 2{μ-η 1:η 3-C α (NMe 2)C β (R′)C γ (H)(R″)}(μ-CO)(CO)(Cp) 2] (R′ = H, R″ = C 6H 5, 3f; R′ = R″ = CO 2Et, 3g). The corresponding reactions of [Ru 2{μ-CN(Me)(CH 2Ph)}(μ-CO)(CO) 2(Cp) 2][SO 3CF 3] ( 1d) with acrylonitrile or methyl acrylate afford the complexes [Ru 2{μ-η 1:η 3-C α (N(Me)(CH 2Ph))C β (H)C γ (H)(R′)}(μ-CO)(CO)(Cp) 2] (R′ = CN, 3h; CO 2Me, 3i), respectively. The coupling reaction of olefin with the carbyne carbon is regio- and stereospecific, leading to the formation of only one isomer. C–C bond formation occurs selectively between the less substituted alkene carbon and the aminocarbyne, and the C β –H, C γ –H hydrogen atoms are mutually trans. The reactions with acrylonitrile, leading to 3a– c and 3h involve, as intermediate species, the nitrile complexes [M 2{μ-CN(Me)(R)}(μ-CO)(CO)(NC–CH CH 2)(Cp) 2][SO 3CF 3] (M = Fe, R = Me, 4a; M = Fe, R = Xyl, 4b; M = Fe, R = 4-C 6H 4OMe, 4c; M = Ru, R = CH 2C 6H 5, 4d). Compounds 3a, 3d and 3f undergo methylation (by CH 3SO 3CF 3) and protonation (by HSO 3CF 3) at the nitrogen atom, leading to the formation of the cationic complexes [Fe 2{μ-η 1:η 3-C α (N(Me) 3)C β (H)C γ (H)(R)}(μ-CO)(CO)(Cp) 2][SO 3CF 3] (R = CN, 5a; R = CO 2Me, 5b; R = C 6H 5, 5c) and [Fe 2{μ-η 1:η 3-C α (N(H)(Me) 2)C β (H)C γ (H)(R)}(μ-CO)(CO)(Cp) 2][SO 3CF 3] (R = CN, 6a; R = CO 2Me, 6b; R = C 6H 5, 6c), respectively. Complex 3a, adds the fragment [Fe(CO) 2(THF)(Cp)] +, through the nitrile functionality of the bridging ligand, leading to the formation of the complex [Fe 2{μ-η 1:η 3-C α (NMe 2)C β (H)C γ (H)(CNFe(CO) 2Cp)}(μ-CO)(CO)(Cp) 2][SO 3CF 3] ( 9). In an analogous reaction, 3a and [Fe 2{μ-CN(Me)(R)}(μ-CO)(CO) 2(Cp) 2][SO 3CF 3], in the presence of Me 3NO, are assembled to give the tetrameric species [Fe 2{μ-η 1:η 3-C α (NMe 2)C β (H)C γ (H)(CN[Fe 2{μ- CN(Me)(R)}(μ-CO)(CO)(Cp) 2])}(μ-CO)(CO)(Cp) 2][SO 3CF 3] (R = Me, 10a; R = Xyl, 10b; R = 4-C 6H 4OMe, 10c). The molecular structures of 3a and 3b have been determined by X-ray diffraction studies.