SYNTHESIS AND CHARACTERIZATION OF COBALT-CAGE COMPLEXES WITH PENDANT PHENOL GROUPS

The synthesis and characterization of four compounds formed from the r eductive amination of m- and o-hydroxybenzaldehyde to 13,16,19-hexaaza bicyclo[6.6.6]eicosane)cobalt(III) are presented. These compounds are the mono- and dialkylated derivatives of the starting cobalt complex. The X-ray crystal structures of each compound, as its fully protonated chloride salt, have been obtained and are reported. The pK(a)'s of th e compounds were determined by nonlinear least-squares analysis of dat a from potentiometric titrations and UV/vis spectrophotometry. The K-a 's of the phenol groups of the compounds are reduced by roughly 1 orde r of magnitude compared to their analogous organic phenols. In the sol id state, the compounds with one pendant phenol group (2, 4) are yello w and adopt the ob(3) conformation of their ethylene diamine rings in their crystal structures, while the compounds with two pendant phenol groups (3, 5) are orange and have the lel(3) conformation in their cry stal structures. Solid-state reflectance UV/vis spectroscopy confirms these structural differences. In water, all four compounds form orange solutions and adopt the lel(3) conformation, as indicated by comparis on of UV/vis spectroscopy and cyclic voltammetry properties with the l iterature.