Some π-(hetero-1,3-diene) complexes LFe(CO)3(L = benzylideneacetone, chalcone, 2′-hydroxychalcone 2,6-dibenzylidenecyclohexanone, and para-substituted cinnamylideneaniline) and L′Fe(CO)4(L′= chalcone, 2′-hydroxychalcone) have been synthesised. The u.v. spectra of the cinnamylideneaniline complexes are discussed. The LFe(CO)3 complexes (L = benzylideneacetone and cinnamylideneaniline) react with strong acid, protonation occurring on the heteroatom.