C–N Coupling of Isocyanide Ligands Promoted by Acetylide Addition to Diiron Aminocarbyne Complexes

The
bis-isocyanide aminocarbyne diiron complexes [Fe2{μ-CN­(Me)­(R)}­(μ-CO)­(CNR′)2(Cp)2]­[SO3CF3] (R =
R′ = Xyl, 1a; R = Me, R′ = Xyl, 1b; R = Xyl, R′ = tBu, 1c; Xyl = 2,6-C6H3Me2) and the analogous
thiocarbyne complex [Fe2{μ-CS­(Me)}­(μ-CO)­(CNXyl)2(Cp)2]­[SO3CF3], 2, were prepared in high yields from [Fe2{μ-C­(E)}­(μ-CO)­(CO)2(Cp)2]­[SO3CF3] [E =
N­(Me)­(R) or SMe, respectively], by reaction with Me3NO
in the presence of the appropriate isocyanide. The addition of LiCCR′′
to 1a–b promoted intramolecular C–N
coupling between the two isocyanide moieties, resulting in the formation
of [Fe2(μ-CO)­{μ-CN­(Me)­(R)}­{μ-C­(NXyl)­N­(Xyl)­C­(CCR′′)}­(Cp)2] (R = Xyl, R″ = Ph, 3a; R = Xyl, R″
= Tol, 3b; R = Me, R″ = Ph, 3c; Tol
= 4-C6H5Me), in ca. 60% yields. The reaction
of 1a with LiCCSiMe3 proceeded with
coupling between two dinuclear units, to give the tetranuclear complex
C2[Fe2(μ-CO)­(Cp)2­{μ-CN­(Me)­(Xyl)}­{μ-C­(NXyl)­N­(Xyl)­C}]2, 4, in 65% yield. The reaction of 2 with LiCCTol resulted in the formation of a mixture of nonidentified
products. The new complexes were purified by alumina chromatography
and fully characterized by analytical techniques, IR and NMR spectroscopy.
The molecular structures of 3b and 4 were
ascertained by X-ray diffraction studies.

双异氰基氨基卡拜二铁配合物[Fe₂{μ-CN(Me)(R)}(μ-CO)(CNR')₂(Cp)₂][SO₃CF₃]（其中Cp为环戊二烯基（cyclopentadienyl, Cp），SO₃CF₃为三氟甲磺酸根（trifluoromethanesulfonate, SO₃CF₃）），具体包括：R=R'=二甲苯基（xylyl, Xyl，即2,6-二甲基苯基2,6-C₆H₃Me₂）时记为1a；R=Me、R'=Xyl时记为1b；R=Xyl、R'=叔丁基（tert-butyl, tBu）时记为1c。与之结构类似的硫代卡拜配合物为[Fe₂{μ-CS(Me)}(μ-CO)(CNXyl)₂(Cp)₂][SO₃CF₃]，记为2。上述配合物均由前体[Fe₂{μ-C(E)}(μ-CO)(CO)₂(Cp)₂][SO₃CF₃][其中E分别对应N(Me)(R)或SMe]与三甲基胺N-氧化物（trimethylamine N-oxide, Me₃NO）在合适异氰基配体存在下反应，以高收率制得。向1a与1b中加入炔锂LiC≡CR''，可促进两个异氰基配体间的分子内C-N偶联反应，生成配合物[Fe₂(μ-CO){μ-CN(Me)(R)}{μ-C(NXyl)N(Xyl)C(C≡CR'')}(Cp)₂]，其中：R=Xyl、R''=苯基（phenyl, Ph）时记为3a；R=Xyl、R''=对甲苯基（p-tolyl, Tol，即4-甲基苯基4-C₆H₅Me）时记为3b；R=Me、R''=Ph时记为3c，目标产物收率约为60%。1a与三甲基硅基乙炔锂（LiC≡CSiMe₃）的反应发生双核单元间的偶联，得到四核配合物C₂[Fe₂(μ-CO)(Cp)₂{μ-CN(Me)(Xyl)}{μ-C(NXyl)N(Xyl)C}]₂，记为4，收率为65%。配合物2与LiC≡CTol的反应仅生成未鉴定产物的混合物。所有新合成的配合物均通过氧化铝柱层析纯化，并借助分析测试技术、红外光谱（IR）与核磁共振光谱（NMR）完成了全面表征。其中，配合物3b与4的分子结构经X射线衍射实验得以确证。