Preparation and structural feature of a novel class of macrocycles containing (η4-diene)Fe(CO)3

Complexation of macrocycles having two 1,3-diene units by iron carbonyls leads to a mixture of trans and cis macrocycles containing two (η4-diene)Fe(CO)3 complexes. The structures of the macrocycles are unambiguously determined by X-ray analysis. In the trans diiron complex macrocycle, the planes of the two η4-diene units are situated in the macrocyclic plane and the two Fe(CO)3 groups are located above and below the macrocyclic plane to each other. In the cis diiron complex macrocycle, however, one of the two η4-diene planes is in the macrocyclic plane and the other is perpendicular to the macrocyclic plane. Both the trans and cis diiron complex macrocycles are conformationally flexible in solution.