Syntheses, characterization, and structural chemistry of biladien-ac-10-one and -bc-5-one metal complexes with 4N or (3N + O) co-ordination

Abstract

Transition-metal(II) complexes have been formed between Cu, Co, Pd, Hg, Cd, Zn and Ni and biladien-bc-5-ones or -ac-10-ones. All show spectroscopic and analytical data in accordance with the formation of 1 : 1 complexes. Reaction of 5- and 10-oxobiladienes with Cu^II, Co^II, Pd^II, Zn^II, Cd^II and Hg^II always gave complexes in which the metal is co-ordinated to the four pyrrole nitrogens (4N co-ordination) and led to a cyclic, helical conformation of the tetrapyrrole ligand. Reaction of biladien-ac-10-ones with Ni^II also gave the 4N-co-ordinated derivative. However, reaction of biladien-bc-5-ones with Ni^II gave two compounds, one being the 4N-co-ordinated complex and other a side product in which the metal is co-ordinated to three pyrrole nitrogens of the conjugated system and to the meso-oxygen atom of the oxobiladiene [(3N + O) co-ordination]. The latter co-ordination type was found to occur only when the C(19) position became substituted by nucleophiles such as OH or OMe leading to steric repulsion of the fourth pyrrole ring away from the metal. Single-crystal structure analyses were made for 10-oxobiladien-ac complexes with 4N co-ordination of Cu^II, Pd^II, Ni^II or Co^II and for 5-oxobiladien-bc complexes with 4N co-rdination of Pd^II, Co^II or Cu^II. These showed tetrahedrally distorted co-ordination geometries in the MN₄ unit. The molecular structures of two nickel complexes of 5-oxobiladien-bc derivatives with square-planar (3N + O) co-ordination have also been determined.