A macrocyclic ligand 5,14-dihydro-6,15-dimethyl-8,17-diphenyldibenzo-[b,i][1,4,8,11]tetraazacyclotetradecine and its nickel(II) complex: Syntheses, reaction mechanism and structures

The template reaction of o-phenylenediamine, 1-benzoylacetone and nickelous acetate tetrahydrate results in two structure isomers, 6,17-dimethyl-8,15-diphenyldibenzo[b,i][1,4,8,11]tetraazacyclotetradecinatonickel (II) (2) and 6,15-dimethyl-8,17-diphenyldibenzo[b,i][1,4,8,11]tetraazacyclotetradecinatonickel (II) (4). However, the latter has been neglected in the previous research because of its low yield in the template reaction. The mechanism of this template reaction is discussed. Though the steric hindrance between the phenyl ring and the benzo ring in 2 is greater than that in 4, the intermediate of the former shows better structural stability than that of the latter, leading to obviously higher final yield of 2 compared with that of 4. n-Butyl alcohol is used artfully to separate the crude product of the template reaction into almost pure 2 and a mixture of 2 and 4 in a mole ratio of 1:5. The free base of 2, 5,14-dihydro-6,17-dimethyl-8,15-diphenyldibenzo[b,i][1,4,8,11]tetraazacyclotetradecine (1), can be synthesized by demetalization of 2 with gaseous HCl. The same treatment to the mixture of 2 and 4 in a mole ratio of 1:5 leads to the free base of 4, 5,14-dihydro-6,15-dimethyl-8,17-diphenyldibenzo[b,i][1,4,8,11]tetraazacyclotetradecine (3). The neglected macrocyclic compounds 3 and 4 have been characterized unambiguously and their single-crystal structures have also been determined by X-ray diffraction analysis for the first time.

Graphical abstractA macrocyclic ligand 5,14-dihydro-6,15-dimethyl-8,17-diphenyldibenzo[b,i][1,4,8,11]tetraazacyclotetradecine and its nickel(II) complex, 6,15-dimethyl-8,17-diphenyldibenzo[b,i][1,4,8,11]tetraazacyclotetradecinatonickel (II), have been synthesized and characterized unambiguously. Their single-crystal structures have also been determined by X-ray diffraction analysis for the first time.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► A template reaction results in a mixture of (E)-Nidmdptaa and (Z)-Nidmdptaa. ► (E)-Nidmdptaa and (Z)-Nidmdptaa are macrocyclic structure isomers. ► (E)-Nidmdptaa is successfully separated from the mixture of isomers. ► (E)-H2dmdptaa, the free base of (E)-Nidmdptaa, is synthesized and characterized. ► The single-crystal structures of (E)-Nidmdptaa and (E)-H2dmdptaa are determined.