Synthesis of tricarbonyliron cyclohexa-2,4-dienone complexes from tosylhydrazones of acyclic dienone complexes. A novel ansa dicarbonyliron complex by intramolecular trapping of reaction intermediates of the cyclocarbonylation reaction

Cyclohexa-2,4-dienones stabilized by coordination to tricarbonyliron are obtained when tosylhydrazones of tricarbonyliron complexed dienones are submitted to the conditions of the Bamford-Stevens reaction (thermolysis in the presence of strong bases). This cyclocarbonylation reaction proceeds most likely via α-diazodiene complexes, and from there via carbenes, which react intramolecularly with a CO ligand, the coordinatively unsaturated iron species so formed being finally stabilized by an external two-electron ligand. The existence of two such hypothetical intermediates could be proven by intramolecular trapping experiments (1,3-dipolar cycloadducts 3, ansa Fe(CO)2 complex 6, structures confirmed by X-ray diffraction).