Abstract
Addition of cyanide ions to the alkynyl(methoxy)carbene complexes [Fe~2~{μ‐CN(Me)(R)}(μ‐CO)(CO){C~α~(OMe)C~β~≡C~γ~R'}(Cp)~2~]^+^ (R = Xyl, R' = Tol, 1a; R = Xyl, R' = Ph, 1b; R = Xyl, R' = Me~3~Si, 1c; R = Me, R' = Tol, 1d; R = Me, R' = Ph, 1e) occurs selectively at C~α~ to afford the 1,1‐disubstituted σ‐propargyl complexes [Fe~2~{μ‐CN(Me)(R)}(μ‐CO)(CO){C(OMe)(CN)(C≡CR')}(Cp)~2~] (R = Xyl, R' = Tol, 2a; R = Xyl, R' = Ph, 2b; R = Xyl, R' = Me~3~Si, 2c; R = Me, R' = Tol, 2d; R = Me,R' = Ph, 2e). Conversely, the stabilised carbanaions[CH(R)~2~]^–^ (R = CN, CO~2~Me) add at the C~γ~ position with subsequent hydrogen migration to C~β~ to give the 1‐σ‐buta‐1,3‐dienyl complexes [Fe~2~{μ‐CN(Me)(Xyl)}(μ‐CO)(CO){C~α~(OMe)=C~β~HC~γ~(Tol)=C~δ~(R)~2~}(Cp)~2~] (R = CN, 3a; CO~2~Me, 3b). No migration is possible in the absence of hydrogen atoms at C~δ~, therefore addition of [C(Me)(CO~2~Me)~2~]^–^ to 1a results in the formation of the σ‐allenyl complex [Fe~2~{μ‐CN(Me)(Xyl)}(μ‐CO)(CO){C~α~(OMe)=C~β~=C~γ~(Tol)C~δ~(Me)(CO~2~Me)~2~}(Cp)~2~] (4). Protonation of the neutral complexes 3b and 4affords the vinyl(methoxy)carbene complexes [Fe~2~{μ‐CN(Me)(Xyl)}(μ‐CO)(CO){C~α~(OMe)C~β~H=C~γ~(Tol)C~δ~(R)(CO~2~Me)~2~}]^+^ (R = H, 5; Me, 6), which exist in solution as mixtures of (E)‐ and (Z)‐isomers in dynamic equilibrium, as shown by VT NMR studies. The cationic complex 6 shows electrophilic behaviour. Thus, addition of CN^–^ results in the σ‐allyl complex [Fe~2~{μ‐CN(Me)(Xyl)}(μ‐CO)(CO){C~α~(OMe)(CN)[C~β~H=C~γ~(Tol)C~δ~(Me)(CO~2~Me)~2~]}(Cp)~2~] (7), whereas the reaction with Me~2~NH affords the vinyl acyl complex [Fe~2~{μ‐CN(Me)(Xyl)}(μ‐CO)(CO){C~α~(O)C~β~H=C~γ~(Tol)C~δ~(Me)(CO~2~Me)~2~}(Cp)~2~] (8). The crystal structures of 2b and 3a·CH~2~Cl~2~ have been determined. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)