Novel phenanthroline-containing trinuclear double-stranded helicates: Self-recognition between helicates with phenanthroline and bipyridine binding sites

The ligands 6,6'-bis[(2-methyl-1,10-phenanthrolin-9-yl)methylenoxymethylenyl] 2,2'-bipyridine (1)- and 2,9-bis[(2-methyl-1,10-phenanthrolin-9-yl)methylenoxymethylenyl]-1,10-phenanthroline (2) were prepared and shown to self-assemble into double-stranded [(L)(2)Cu-3](3+)-type helicates upon reaction with Cu+. Although the reaction of 1 with AgCF3SO3 afforded the double-stranded helicate [(1)(2)Ag-3](3+), reaction of 2 with this salt yielded a mixture of several complexes, all of apparently double-strand nature, based on their diffusion coefficients. Addition of a large excess of AgCF3SO3 afforded [(2)(2)Ag-3](3+) as the sole product. In addition, it was found that the reaction of Cu+ with mixtures of 1 and 6 ",6'''-bis[(6-methyl-2,2'-bipyridin-6'-yl)methylenoxymethylenyl]-2 ",2'''-bipyridine (4) or of 2 with 2,9-bis[(6-methyl-2,2-bipyridin-6'-yl)methylenoxymethylenyl]-1,10-phenanthroline (3) afforded mixtures of homoleptic and heteroleptic helicates. Helicate distribution seems to follow statistical expectations. Mixing of the double-stranded copper helicates of 2 and 3 in DMSO-d(6) afforded, after 2 weeks, a statistical mixture of the homoleptic and heteroleptic helicates, i.e., [(2)(2)Cu-3](3+), [(3)(2)Cu-3](3+), and [(2/3)Cu-3](3+). However, a statistical mixture was obtained within minutes from the double-stranded silver helicates of 2 and 3 in CD3CN. We conclude therefore that even 2 and 3, which contain three phenanthroline and three bipyridine binding sites, are not "sufficiently instructed" to avoid the formation of a heteroleptic helicate in the course of their self-assembly process.