A macrocyclic approach to transition metal and uranyl Pacman complexes

Multielectron redox chemistry involving small molecules such as O-2, H2O, N-2, CO2, and CH4 is intrinsic to the chemical challenges surrounding sustainable, low-carbon energy generation and exploitation. Compounds with more than one metal reaction site facilitate this chemistry by providing both unique binding environments and combined redox equivalents. However, controlling the aggregation of metal cations is problematic, as both the primary coordination spheres of the metals and the metal-metal separations have to be defined carefully. We described recently a series of pyrrole-based macrocyclic ligands designed to manage metal aggregation and form molecular multimetallic complexes. In particular, we have shown that these compartmentalised Schiff-base calixpyrroles generally form rigid Pacman complexes that prescribe well-defined, metallo microenvironments within the molecular cleft. This article will review the development of this chemistry and its context, and will highlight structural facets and reaction chemistry of metal complexes from across the periodic table.