New avenues for redox-active ligands: Non-classical reactivity with late transition metals facilitated by o-aminophenol derived architectures

Many homogeneous and heterogeneous catalyst systems contain one or more transition metals. The widespread employment of these metals as catalysts is ascribed to their accessible d-orbitals to activate chemical bonds, and the ability to undergo metal-based oxidation state changes to facilitate desirable chemical transformations. The fine-tuning of homogeneous catalyst systems is commonly achieved by the coordination of (spectator) ligands, which can vary greatly in steric bulk or electron-donating ability. For such ligands the energy required for oxidation or reduction of the ligand is much bigger than that needed to change the oxidation state of the metal. Accordingly, the redox changes required for bond making and breaking processes typically occur at the metal center. Redox-active ligands have more energetically accessible levels for reduction and/or oxidation upon coordination to a metal. As a result, either solely ligand-centered redox processes can occur, with the metal center remaining in the same oxidation state, or more diffuse scenarios, wherein both the ligand and metal change oxidation states in a synergistic fashion. Although initially thought of as a spectroscopic curiosity, redox-active ligands are nowadays recognized for their ability to induce new reactivity at metal centers. Within this thesis we have shown that o-aminophenol derived architectures can give fascinating spectroscopic properties upon coordination to late transition metals. Moreover, these ligands can expand upon a metal’s "common" reactivity by actively taking part in intramolecular redox processes. We have demonstrated that intramolecular single-electron transfer processes can facilitate homolytic bond cleaving reactions and the generation of reactive nitrogen-centered radicals

Data underlying the research of: Tuning the Bonding of a µ-Mesityl Ligand on Dicopper(I) through a Proton-Responsive Expanded PNNP Pincer Ligand

The files contain the Nuclear Magnetic Resonance spectra of all compounds reported, and input/output files of the ORCA calculations within this publicatio

New avenues for ligand-mediated processes: expanding metal reactivity by the use of redox-active catechol, o-aminophenol and o-phenylenediamine ligands

Redox-active ligands have evolved from being considered spectroscopic curiosities - creating ambiguity about formal oxidation states in metal complexes - to versatile and useful tools to expand on the reactivity of (transition) metals or to even go beyond what is generally perceived possible. This review focusses on metal complexes containing either catechol, o-aminophenol or o-phenylenediamine type ligands. These ligands have opened up a new area of chemistry for metals across the periodic table. The portfolio of ligand-based reactivity invoked by these redox-active entities will be discussed. This ranges from facilitating oxidative additions upon d(0) metals or cross coupling reactions with cobalt(III) without metal oxidation state changes - by functioning as an electron reservoir - to intramolecular ligand-to-substrate single-electron transfer to create a reactive substrate-centered radical on a Pd(II) platform. Although the current state-of-art research primarily consists of stoichiometric and exploratory reactions, several notable reports of catalysis facilitated by the redox-activity of the ligand will also be discussed. In conclusion, redox-active ligands containing catechol, o-aminophenol or o-phenylenediamine moieties show great potential to be exploited as reversible electron reservoirs, donating or accepting electrons to activate substrates and metal centers and to enable new reactivity with both early and late transition as well as main group metals

Selective Conversion of CO2 into Isocyanate by Low-Coordinate Iron Complexes

Discovery of the mechanisms for selective trans formations of CO2 into organic compounds is a challenge. Herein, we describe the reaction of low-coordinate Fe silylamide complexes with CO2 to give trimethylsilyl isocyanate and the corresponding Fe siloxide complex. Kinetic studies show that this is a two-stage reaction, and the presence of a single equivalent of THF influences the rates of both steps. Isolation of a thermally unstable intermediate provides mechanistic insight that explains both the effect of THF in this reaction, and the way in which the reaction achieves high selectivity for isocyanate formation

Redox-Active-Ligand-Mediated Formation of an Acyclic Trinuclear Ruthenium Complex with Bridging Nitrido Ligands

Coordination of a redox‐active pyridine aminophenol ligand to RuII followed by aerobic oxidation generates two diamagnetic RuIII species [1 a (cis) and 1 b (trans)] with ligand‐centered radicals. The reaction of 1 a/1 b with excess NaN3 under inert atmosphere resulted in the formation of a rare bis(nitrido)‐bridged trinuclear ruthenium complex with two nonlinear asymmetrical Ru‐N‐Ru fragments. The spontaneous reduction of the ligand centered radical in the parent 1 a/1 b supports the oxidation of a nitride (N3−) to half an equivalent of N2. The trinuclear omplex is reactive toward TEMPO‐H, tin hydrides, thiols, and dihydrogen