Tricarbonyliron complexes derived from dimethyl 1,3-butadiene-2,3-dicarboxylate: formation of [Fe(CO)3]2–dimethyl 1,3-butadiene-2,3-dicarboxylate

Treatment of dimethyl 1,3-butadiene-2,3-dicarboxylate with Fe 2 (CO) 9 provided the corresponding tricarbonyl(η 4 -dimethyl 1,3-butadiene-2,3-dicarboxylato-O)iron, [Fe(C 8 H 10 O 4 )(CO) 3 ], (II), as the main product and the novel μ-[(1,2-η,κO 3 :3,4-η,κO 2 )-dimethyl 1,3-butadiene-2,3-dicarboxylato]bis(tricarbonyliron), [Fe 2 (C 8 H 10 O 4 )(CO) 6 ], (III). In the crystal structure of (II), the electron-deficient butadiene complexes with one Fe(CO) 3 group, whereas in (III), the butadiene adopts an unusual conformation and forms a complex with two Fe(CO) 3 groups. In (III), each Fe atom possesses a trigonal bipyramidal geometry, with one olefinic bond and two carbonyl ligands occupying the basal positions, and the keto oxygen of the ester and the other carbonyl ligand occupying apical positions.