Metalloporphenes: Synthesis and Characterization

University Of Colorado At Boulder, Boulder CO

Investigators

Abstract

In this project, funded by the Chemical Structure, Dynamics & Mechanisms B Program of the Chemistry Division, Professor Josef Michl of the Department of Chemistry at the University of Colorado, Boulder, is introducing various metal ions into a thin sheet (single atomic layer thick) of a new polymer resembling a single sheet of graphene (a form of carbon found in pencils), and exploring the resulting chemical properties. Like graphene, which consists of fully fused six-membered carbon (benzene) rings, the new two-dimensional polymer, porphene, consists of an array of fused rings made up of the macrocyclic heterocycle, porphyrin (which contains carbon, nitrogen and often metals). Unlike graphene, porphene can be modified without removing the bonding which causes its special electronic or reactivity properites. The goal of this research is to exploit the expected characteristics of this very recently prepared, unusual material for the development of new electrocatalysts and photocatalysts for water splitting, conversion of carbon dioxide into fuels, and other processes that permit the conversion of solar energy into stored chemical energy. The project lies at the interface of organic, inorganic, and materials chemistry. Professor Michl's group is well positioned to provide the highest level of education and training for students underrepresented in science and to arouse interest in science among K-12 students through outreach activities. Like graphene, which consists of fully conjugated fused benzene rings, the new two-dimensional polymer, porphene, consists of an array of fully conjugated fused rings made up of the macrocyclic heterocycle, porphyrin. Unlike graphene, porphene can be functionalized without removing the conjugation of any of the atoms that participate in its pi-electron system. This flexibility in functionalization is accomplished by insertion of metal ions into the centers of the porphyrin rings. Similar to the ordinary, monomeric porphyrins, the metal ions in porphene may be able to carry two, one, or zero ligands of almost arbitrary structure, permitting a conversion of the parent free-base porphene into a large family of two-dimensional metallopolymers with easily tuneable chemical, electrochemical, and photochemical catalytic properties. The syntheses include modifications designed to probe the relationships between molecular structures and various catalytic properties. The research addresses several questions: How can the presently available double layer of porphene be exfoliated to single layers? Which transition and main-group metal ions can be inserted into free-base porphene layers and under what conditions are they removed? What ligands can these metal ions carry? Other questions examine the reactivity of porphene: How do the reactions that occur on the metal ions contained in porphene differ from those known from studies of ordinary monomeric metalloporphyrins in solution? Can any of the observed reactivity be utilized to construct catalytic cycles? Particular attention will be paid to processes in which a metalloporphene is used to cover the surface of a light-absorbing material or the surface of an electrode. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.