Design of Organoiron Macromolecules Based on Upper Rim Functionalized Calix[4]arenes

The versatility of cationic cyclopentadienyliron complexes is demonstrated for the generation of calix[4]arene-based dendrimers and polymers. Dendrimers were prepared from a branched organoiron calix[4]arene through subsequent reactions of azo dyes and organoiron complexes. The resulting azo dye-containing metallocalix[4]arenes were soluble in polar organic solvents and displayed λ(max) ranging between 430 and 456 nm. Upon addition of various acids, the λ(max) shifted to higher wavelengths (513-535 nm). In the solid state and in solution, the azo dye-containing metallocalix[4]arenes reversibly changed colour in the presence of acid and base, indicating their potential use as acid sensors. Cyclic voltammetric studies showed that the iron centres of the metallocalix[4]arenes were reversibly reduced at E(1/2)  = -1.49 V. When non-branching organoiron-based calix[4]arene were reacted with dithiols, polymers containing calix[4]arenes either in their side chains or main chains were obtained. The polymers possessed weight average molecular weights between 35 000 and 53 000. The polymers were determined to be thermally stable with backbone decomposition occurring above 500 °C.