Synthesis and a high field NMR study of a 2,2'-bipyridyl substituted ?-cyclodextrin and its luminescent rhenium(I) metal complex

The synthesis and an NMR spectroscopic study of the substituted bipyridine deriv. I (R = 6-?-(per-OMe)-cyclodextrin), and the metal complex II are reported. The ligand I was prepd. by condensation of monohydroxypermethylated ?-cyclodextrin with 6-bromomethyl-2,2'-bipyridine under std. Williamson reaction conditions. The neutral complex II was obtained by treatment of the ligand I with Re(CO)5Br. 600 MHz two-dimensional NMR expts. (DQF-COSY, HOHANA, ROESY) were used to establish the purity and structure of the ligand I and complex II in CDCl3. While CD measurements suggest that the metal is directed over the cavity, NOE connectivities between the bipyridyl protons and the surface of the cyclodextrin cavity were not detected in ROESY expts. Preorganized assemblies based on II, in which the metal is directed over the cavity, provide ideal systems in which to study photochem. communication between the photoactive unit and a guest mol. encapsulated in the cyclodextrin cavity. [on SciFinder(R)]