Tripyrrindione as a Redox‐Active Ligand: Palladium(II) Coordination in Three Redox States

Abstract

The tripyrrin-1,14-dione scaffold of urinary pigment uroerythrin coordinates divalent palladium as a planar tridentate ligand. Spectroscopic, structural and computational investigations reveal that the tripyrrindione ligand binds as a dianionic radical, and the resulting complex is stable at room temperature. One-electron oxidation and reduction reactions do not alter the planar coordination sphere of palladium(II) and lead to the isolation of two additional complexes presenting different redox states of the ligand framework. Unaffected by stability problems common to tripyrrolic fragments, the tripyrrindione ligand offers a robust platform for ligand-based redox chemistry.

Interactions of Metal-Based and Ligand-Based Electronic Spins in Neutral Tripyrrindione π Dimers

“…33 Correspondingly, the reaction of [Cu(TD1 • )(H 2 O)] with AgBF 4 (Scheme 1) led to a ligand-based oxidation and formation of a new species, in line with our previous observations for the palladium complex. 33 …”

“…33–35 We discovered that the tripyrrindione ligand H 3 TD1 (Chart 1) coordinates Pd(II) as a planar radical dianion. 33 The ligand-based radical in the resulting complex [Pd(TD1 • )(H 2 O)] (in which the fourth coordination position is occupied by a water molecule) is delocalized on the tridentate pyrrole-based scaffold and is stable at room temperature. Notably, this system undergoes reversible ligand-based one-electron processes and can be isolated in three different redox states.…”

Hexaethyltripyrrindione (H3Et6tpd): A Non‐Innocent Ligand Forming Stable Radical Complexes with Divalent Transition‐Metal Ions

“…The molecular identities and the presence of the aquo ligand were confirmed in all cases by combustion analyses and ESI mass spectrometry. The palladium complex 2 was identical to the species described previously and mentioned in the Introduction …”

“…Table provides an overview of selected X‐ray diffraction data. A structural analysis of one polymorph of 2 crystallizing in the triclinic system, space group P 1, has been published before, and is discussed here for comparison (entry II in Table ). On the molecular level, the structural parameters found for the different polymorphic and solvate forms of each metal ion are very similar and within experimental error.…”

Transition from a Metal‐Localized Mixed‐Valence Compound to a Fully Delocalized and Bridge‐Biased Electrophore in a Ruthenium–Amine–Ruthenium Tricenter System

“…[2][3][4][5][6][7][8][9][10][11][12] Furthermore, these redox-active complexes are useful molecular materials for applications such as molecular electronics, [13] near-infrared electrochromism, [14] redox switches, [15] and molecular logic gates and memories.…”