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

The bridging aminocarbyne complexes [Fe2{μ-CN(Me)(R)}(μ-CO)(CO)2(Cp)2][SO3CF3] (R = Me, 1a; Xyl, 1b; 4-C6H4OMe, 1c; Xyl = 2,6-Me2C6 H3) react with acrylonitrile or methyl acrylate, in the presence of Me3NO and NaH, to give the corresponding μ-allylidene complexes [Fe2{μ-η1:η3- Cα(N(Me)(R))Cβ(H)Cγ(H)(R′)}(μ-CO)(CO)(Cp)2] (R = Me, R′ = CN, 3a; R = Xyl, R′ = CN, 3b; R = 4-C6H4OMe, R′ = CN, 3c; R = Me, R′ = CO2Me, 3d; R = 4-C6H4OMe, R′ = CO2Me, 3e). Likewise, 1a reacts with styrene or diethyl maleate, under the same reaction conditions, affording the complexes [Fe2{μ-η1:η3-Cα(NMe2)Cβ(R′)Cγ(H)(R″)}(μ-CO)(CO)(Cp)2] (R′ = H, R″ = C6H5, 3f; R′ = R″ = CO2Et, 3g). The corresponding reactions of [Ru2{μ-CN(Me)(CH2Ph)}(μ-CO)(CO)2(Cp)2][SO3CF3] (1d) with acrylonitrile or methyl acrylate afford the complexes [Ru2{μ-η1:η3-Cα(N(Me)(CH2Ph))Cβ(H)Cγ(H)(R′)}(μ-CO)(CO)(Cp)2] (R′ = CN, 3h; CO2Me, 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 Cβ–H, Cγ–H hydrogen atoms are mutually trans. The reactions with acrylonitrile, leading to 3a–c and 3h involve, as intermediate species, the nitrile complexes [M2{μ-CN(Me)(R)}(μ-CO)(CO)(NC–CHdouble bond; length as m-dashCH2)(Cp)2][SO3CF3] (M = Fe, R = Me, 4a; M = Fe, R = Xyl, 4b; M = Fe, R = 4-C6H4OMe, 4c; M = Ru, R = CH2C6H5, 4d). Compounds 3a, 3d and 3f undergo methylation (by CH3SO3CF3) and protonation (by HSO3CF3) at the nitrogen atom, leading to the formation of the cationic complexes [Fe2{μ-η1:η3-Cα(N(Me)3)Cβ(H)Cγ(H)(R)}(μ-CO)(CO)(Cp)2][SO3CF3] (R = CN, 5a; R = CO2Me, 5b; R = C6H5, 5c) and [Fe2{μ-η1:η3-Cα(N(H)(Me)2)Cβ(H)Cγ(H)(R)}(μ-CO)(CO)(Cp)2][SO3CF3] (R = CN, 6a; R = CO2Me, 6b; R = C6H5, 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 [Fe2{μ-η1:η3-Cα(NMe2)Cβ(H)Cγ(H)(CNFe(CO)2Cp)}(μ-CO)(CO)(Cp)2][SO3CF3] (9). In an analogous reaction, 3a and [Fe2{μ-CN(Me)(R)}(μ-CO)(CO)2(Cp)2][SO3CF3], in the presence of Me3NO, are assembled to give the tetrameric species [Fe2{μ-η1:η3-Cα(NMe2)Cβ(H)Cγ(H)(CN[Fe2{μ- CN(Me)(R)}(μ-CO)(CO)(Cp)2])}(μ-CO)(CO)(Cp)2][SO3CF3] (R = Me, 10a; R = Xyl, 10b; R = 4-C6H4OMe, 10c). The molecular structures of 3a and 3b have been determined by X-ray diffraction studies.