Coupling of Isocyanide and mu-Aminocarbyne Ligands in Diiron Complexes Promoted by Hydride Addition

The diiron μ-aminocarbyne complexes [Fe2{μ-CN(Me)(R)}(μ-CO)(CO)(CNR′)(Cp)2][SO3CF3] (R = R′ = Xyl, 2a; R = Xyl, R′ = Me, 2b; R = Xyl, R′ = But, 2c; R = Xyl, R′ = p-C6H4CF3, 2d; R = Me, R′ = Xyl, 2e; Xyl = 2,6-Me2C6H3), containing an isocyanide ligand, have been obtained via CO replacement with the appropriate CNR′ ligand from [Fe2{μ-CN(Me)(R)}(μ-CO)(CO)2(Cp)2][SO3CF3] (R = Xyl, 1a; R = Me, 1b). Compound 2a, upon treatment with NaBH4 and heating at reflux temperature in THF solution, is transformed into the aminocarbene–aldimine [Fe2{μ-η1(C):η1(N)-CN(Me)(Xyl)CH═N(Xyl)}(μ-CO)2(Cp)2] (3) in moderate yield. The reactions occurs via formation of the formimidoyl complex [Fe2{μ-CN(Me)(Xyl)}(μ-CO)(CO){C(H)═NXyl}(Cp)2] (4a), which has been isolated by reacting 2a with NaBH4 at 0 °C. Likewise, the formimidoyl complex [Fe2{μ-CN(Me)(R)}(μ-CO)(CO){C(H)═NR′}(Cp)2] (R = Xyl, R′ = Me, 4b; R = Me, R′ = Xyl, 4c) have been obtained from 2b,e, respectively, upon reaction with NaBH4, but these complexes do not convert into the aminocarbene–aldimine complexes analogous to 3. Reactions of 2a with other nucleophiles have been investigated, without obtaining any product similar to 3. Complex 2a reacts with NaCN or with LiPPh2, resulting in isocyanide displacement and formation of [Fe2{μ-CN(Me)(Xyl)}(μ-CO)(CO)(CN)(Cp)2] (5) and [Fe2{μ-CN(Me)(Xyl)}(μ-CO)(CO)(PPh2)(Cp)2] (6), respectively. Addition of the organocopper reagent Li2CuCNMe2 to 2a affords the acyl complex [Fe2{μ-CN(Me)(Xyl)}(μ-CO){C(O)Me}(CNXyl)(Cp)2] (7). The thiocarbyne complex [Fe2{μ-CSMe}(μ-CO)(CO)(CNXyl)(Cp)2][SO3CF3] (8), which shows analogies with 2a, reacts with NaBH4, affording the carbene derivative [Fe2 μ-{C(SMe)(H)}(μ-CO)(CO)(CNXyl)(Cp)2] (9). The molecular structures of 2a and 3 have been determined by X-ray diffraction studies.