Gram-Scale,\nOne-Pot Synthesis of a Cofacial Porphyrin\nBridged by Ortho-xylene as a Scaffold for Dinuclear Architectures

Herein, we report the reaction between four 1,2-dibromoxylenes\nand two tetra-3-pyridylporphyrins for the formation of a cofacial\nporphyrin core spanned by dipyridinium xylene moieties. The metal-free\norganic nanocage (oNC) was synthesized in one twenty-four h step at\na gram-scale with a 91.5% yield. The <b>free base oNC</b> was\nsubsequently metalated with cobalt(II) (<b>Co-oNC</b>), copper(II)\n(<b>Cu-oNC</b>), and nickel(II) (<b>Ni-oNC</b>) ions to\nfurnish dinuclear complexes that were characterized by mix of mass\nspectrometry, NMR, EPR, electronic absorption spectroscopy, and for <b>Co-oNC</b>, single-crystal X-ray diffraction. Cofacial cobalt\nporphyrins are often active as catalysts for the Oxygen Reduction\nReaction. Under heterogeneous conditions in water, <b>Co-oNC</b> was 83% selective for the electrocatalytic 4 e<sup>–</sup>/4 H<sup>+</sup> reduction of O<sub>2</sub> to H<sub>2</sub>O, matching\nhomogeneous experiments which revealed consistent selectivity for\nH<sub>2</sub>O (88%). This oNC core offers significant advantages\nover prisms formed by coordination-driven self-assembly: the dipyridnium-xylene\ncoupling can furnish over 1 g of material in a single synthesis and\nthe tethering motif is robust, maintaining a cofacial architecture\nin acidic and basic solutions. We envision this approach may be generalized\nto other bis-bromobenzyl building blocks, providing a means to tune\nmetal–metal separation and other structural and electronic\nproperties.