C,H bond activation of imino substituted heterocycles: Synthesis and crystal structure of [μ2-η3-( R) N-CH2-C=C-C(H) =C(H)-X ]Fe2( CO) 6 and the isomeric clusters [μ2-η3-(R)N-CH2-C=C-X-C(R′)=C(R″)]Fe2(CO)6

Article abstract of DOI:10.1016/S0022-328X(96)06824-6

The reaction of Fe₂(CO)₉ with heterocyclic imines derived from thiophene-2-carbaldehyde or N-methyl-pyrrole-2-carbaldehyde produces the dinuclear compounds [μ₂-η³-(R)N-CH₂-C=C-C(H)-X(H)-X]Fe₂(CO)₆ (R = Ph, C₆H₁₁, p-^tBu-C₆H₄; X = S, NMe). The analogous reaction with imines of thiophene-3-carbaldehyde or indole-3-carbaldehyde yields the corresponding isomeric clusters [μ₂-η³-(R)N-CH₂-C=C-X-C(R′)=C(R″)Fe₂(CO)₆ (R = Ph, C₆H₁₁, R′ = R″ = H, X = S; R = Ph, p-^tBu-C₆H₄, R′ = R″ = -C₆H₄-, X = NH). The reaction proceeds via activation of the C,H bond in β-position relative to the exocyclic C,N double bond of the imine ligands. A 1,3 hydrogen shift reaction then leads to the formation of a methylene group instead of the former imine carbon atom. So, the imine ligands are transformed into μ₂-η³-enyl-amido ligands being coordinated to an Fe₂(CO)₆ moiety, which is confirmed by X-ray structure analyses of six compounds.