Iron carbonyl complexes from 2-[2,3-diaza-4-(2-thienyl)buta-1,3-dienyl]thiophene: NN bond cleavage and cyclometalation

When thienyl Schiff base 1, derived from 2-formylthiophene and hydrazine, reacted with Fe2(CO)9 in n-hexane, three major complexes were obtained: (1) a diironhexacarbonyl complex with two 2-thienylmethylideneamido bridging ligands 2, which resulted from the NN bond cleavage of ligand 1; (2) a doubly cyclometalated di-μ-di-(η1:η2-thienyl; η1:η1(N))bis(hexacarbonyldiiron) complex (3); and (3) a cyclometalated (μ-η1:η2-thienyl; η1:η1(N))hexacarbonyldiiron complex (4). Molecular structures of compounds 1a, 1c, and 2a have been determined by single-crystal X-ray diffraction.