Synthesis of dipyrrins bearing chirality adjacent to the conjugated skeleton - Electron-poor pyrroles exhibit dramatically reduced nucleophilicity

Abstract

With the aim of furthering our investigations into the asymmetric complexation of dipyrrinato ligands, a dipyrrin bearing a stereogenic centre directly adjacent to the conjugated skeleton was synthesized. The electron- withdrawing nature of the chiral 4-(2,2,2-trifluoro-1-hydroxyethyl)- substituent significantly reduced the nucleophilicity of corresponding pyrroles, such that 2,2'-symmetrically substituted bis(dipyrrin)s bearing this motif were inaccessible. Furthermore, solutions of mononuclear dipyrrinato complexes were found to be less stable to acid-catalyzed decomplexation than the corresponding dinuclear complexes.