Coupling of Isocyanide and μ‑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.