Metallo-porphyrin containing zirconium phosphonate thin films: Structure and catalysis

Thin films containing mono- and tetra-phosphonic acid palladium tetraphenyl porphyrins and tetra-phosphonic acid manganese tetraphenyl porphyrins, PdP1, PdP4, and MnP4, were prepared by both Langmuir-Blodgett (LB) and self-assembly (SA) techniques. Within the hydrophilic regions of these films was incorporated a zirconium phosphonate network which lent significant stability and flexibility of preparation to these films.;In the LB films of the palladium porphyrins, it was found that the monophosphonic acid porphyrins aggregated under all film preparation conditions and in solutions at high concentrations. However, the chromophore aggregation could be controlled in the tetra-phosphonic acid porphyrins when the films were transferred at mean molecular areas greater or near the mean molecular area of the chromophore itself. Self-assembling the PdP4 was another means of controlling the chromophore interaction in the films. Because chromophore aggregation was expected to inhibit catalysis, film preparation conditions were sought in order to avoid this.;The LB and SA films of pure manganese porphyrins were successfully prepared by a number of different methods. Aggregation appeared insignifcant when transferred at high mean molecular areas and when the films were self-assembled. The pure manganese porphyrin films were successful at catalyzing the epoxidation of cyclooctene using iodosylbenzene as the oxidant.;To activate the porphyrin for catalysis with peroxide oxidants, a heterocyclic ligand was also incorporated into the manganese porphyrin containing films. The heterocyclic ligand used was an imidazole substituted with an octadecylphosphonic acid chain. Both the manganese porphyrin and the imidazole amphiphile were tethered to a zirconium phosphonate network, first for ease of film synthesis and second, to stabilize the film for use in the catalysis reactions.;Though significant catalyst degradation has been reported in homogeneous and alternative heterogeneous catalysis studies, the manganese porphyrin and imidazole containing zirconium phosphonate films were generally more resistant to degradation under catalysis conditions. The stability of the films toward epoxidation conditions has led to easily recyclable catalysts.