Toward the Synthesis of a Topologically Non-Planar Porphyrin

Abstract

Topology is an area of mathematics concerned with spatial properties that are preserved under deformation. When applied to chemistry it allows stretching of bonds and bending of structure, but no breaking. A topologically planar molecule is one that has been deformed to become planar; however, there cannot be any crossing over between bonds. A porphyrin molecule is a macrocyclic organic molecule that consists of four pyrroles attached to each other by methine bridges. In order to have a topologically non-planar porphyrin, two straps must be introduced in order to bridge the molecule. Addition of a metal to the center of the molecule results in a topologically non-planar porphyrin. The synthetic route to the base porphyrin started with α-bromo-ο-tolunitrile and sodium methoxide to produce α-methoxy-ο tolunitrile. The tolunitrile was reduced with dibal and hydrolyzed with hydrochloric acid/water to form α-methoxy-ο-tolualdehyde. Subsequently, the tolualdehyde was combined with pyrrole to form a ?half porphyrin,? called a dipyrromethane. The final step in the synthesis of the base porphyrin combined the dipyrromethane and α-bromo-ο-tolualdehyde, with boron trifluoride catalyst. Different atropisomers were characterized by ?H NMR as the methoxy groups exhibited varying chemical shifts and peaks. Heating the porphyrin to 70?C appeared to rotate the methoxy groups, overcoming the problem of having multiple atropisomers. Various attempts at introducing straps to the base porphyrin have been inconclusive.