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.