Metal complexes immobilized within porous polymer hosts: Applications to reversible dioxygen binding

The research described in this dissertation involves control of the stereochemistry and microenvironment around Co(II) ions by immobilization within a porous polymer host. The technique used to fabricate these materials is template copolymerization. In this technique a template metal complex is rationally designed and synthesized, and then immobilized within a porous polymeric host. The immobilization is performed by utilizing the principles of molecular imprinting, to yield sites within polymeric materials which have the same shape and size as the template (imprint) compound. Co(II) containing materials made by this approach are able to reversibly bind dioxygen.; Chapter 2 discusses the chemistry of an immobilized site designed to enforce a square pyramidal geometry around Co(II) ions. An unsymmetrical Co(III) complex was designed for this purpose that contained different axial ligands. This complex, which is exchange inert and diamagnetic has been thoroughly characterized using various spectroscopic techniques, including NMR spectroscopy. The complex was immobilized within a mesoporous polymer host by the template copolymerization approach. The polymer obtained was chemically modified at the immobilized metallated sites to generate a material capable of reversible dioxygen binding. Two different chemical modification routes have been explored, one of which is hydrolytic, while the other is reductive. Results are presented to show that the ligands are predisposed to bind a metal ion in a square pyramidal fashion. However, an equilibrium between four and five coordinate Co(II) sites is found, which is similar to what is observed for molecular analogs in solution. This equilibrium is dependent on Co(II) sites is observed when the polymer is suspended in nitromethane, the solvent used to synthesize the original template immobilized polymer. Results are also presented which show that nearly 90% of these Co(II) sites reversibly bind dioxygen in a variety of suspending solvents. This is a significant improvement over related polymer immobilized, or zeolite encapsulated systems.; Chapter 3 explores the chemistry arising from a bimodal approach to the synthesis of Co(II) sites within a mesoporous polymer host. The design of this system involves control of both the primary and secondary coordination spheres around Co(II) ions. A modified urea axial base containing Co(III) Schiff base complex has been utilized. This complex has been utilized to form hydrogen bonds to a diamide group containing crosslinker molecule. This system is more complex in design than the system discussed in Chapter 2. This complex has been copolymerized with the diamide crosslinker to obtain a porous polymer in which the amide bonds from the crosslinker may be used to hydrogen bond to the Co-O₂ adducts formed in the immobilized cavities. EPR spectroscopy has been used to probe the formation of hydrogen bonds from dioxygen molecules which are covalently bound to the metal, to either the amide bonds on the polymer walls, or to an ordered array of solvent molecules.; Chapter 4 involves a system obtained via surface grafting of the mixed axial ligand containing complex described in Chapter 2 onto a porous support polymer. Once again, chemical modification of the metallated sites on the polymer surface and remetallation with Co(II) ions has been studied. These sites have also been probed for their reversible dioxygen binding properties. The two systems have been compared with respect to metal loading, site architecture, and ability of the polymer host to effectively isolate the metallated sites.