Gold Tripyrrindione:\nRedox Chemistry and Reactivity\nwith Dichloromethane

The identification of ligands that stabilize Au(III)\ncenters has\nled to the isolation of complexes for applications in catalysis, gold-based\ntherapeutics, and functional materials. Herein, we report the coordination\nof gold by tripyrrin-1,14-dione, a linear tripyrrole with the scaffold\nof naturally occurring metabolites of porphyrin-based protein cofactors\n(e.g., heme). Tripyrrindione H<sub>3</sub>TD2 binds Au(III) as a trianionic\ntridentate ligand to form square planar complex [Au(TD2)(H<sub>2</sub>O)], which features an adventitious aqua ligand. Two reversible ligand-based\noxidations of this complex allow access to the other known redox states\nof the tripyrrindione framework. Conversely, (spectro)electrochemical\nmeasurements and DFT analysis indicate that the reduction of the complex\nis likely metal-based. The chemical reduction of [Au(TD2)(H<sub>2</sub>O)] leads to a reactive species that utilizes dichloromethane in\nthe formation of a cyclometalated organo-Au(III) complex. Both the\naqua and the organometallic Au(III) complexes were characterized in\nthe solid state by microcrystal electron diffraction (MicroED) methods,\nwhich were critical for the analysis of the microcrystalline sample\nof the organo-gold species. Overall, this study illustrates the synthesis\nof Au(III) tripyrrindione as well as its redox profile and reactivity\nleading to gold alkylation chemistry.