Julia R. Khusnutdinova

Direct C(sp3)−O Reductive Elimination of Olefin Oxides from PtIV-Oxetanes Prepared by Aerobic Oxidation of PtII Olefin Derivatives (Olefin = cis-Cyclooctene, Norbornene)

Internal olefins, cis-cyclooctene and norbornene, react with (dpms)PtII(OH)(ethene) in water to produce PtII oxetanes (norbornene) or hydroxo olefin complexes (cis-cyclooctene); both produce anionic PtII oxetanes in basic solutions; their subsequent aerobic oxidation cleanly furnishes corresponding PtIV oxetanes that undergo direct C(sp3)−O reductive elimination of olefin oxides in various solvents and in the solid-state that is unprecedented for PtIV.

Oxidant-free conversion of cyclic amines to lactams and H2 using water as the oxygen atom source

Direct conversion of cyclic amines to lactams utilizing water as the only reagent is catalyzed by pincer complex 2. In contrast to previously known methods of amine-to-amide conversion, this reaction occurs in the absence of oxidants and is accompanied by liberation of H2, with water serving as a source of oxygen atom. Formation of a cyclic hemiaminal intermediate plays a key role in enabling such reactivity. This represents an unprecedented, conceptually new type of amide formation reaction directly from amines and water under oxidant-free conditions.

Mechanistic Investigations of the Catalytic Formation of Lactams from Amines and Water with Liberation of H2

The mechanism of the unique lactam formation from amines and water with concomitant H2 liberation with no added oxidant, catalyzed by a well-defined acridine-based ruthenium pincer complex was investigated in detail by both experiment and DFT calculations. The results show that a dearomatized form of the initial complex is the active catalyst. Furthermore, reversible imine formation was shown to be part of the catalytic cycle. Water is not only the oxygen atom source but also acts as a cocatalyst for the H2 liberation, enabled by conformational flexibility of the acridine-based pincer ligand.

The Conformational Flexibility of the Tetradentate Ligand tBuN4 is Essential for the Stabilization of (tBuN4)PdIII Complexes

The conformationally flexible tetradentate pyridinophane ligand (tBu)N4 effectively lowers the oxidation potential of ((tBu)N4)Pd(II) complexes and promotes their facile chemical and electrochemical oxidation, including unpredecented aerobic oxidation reactivity. While the low potential of a number of Pd(II) (and Pt(II)) complexes supported by various fac-chelating polydentate ligands is often attributed to the presence of a coordinating group in the axial position of the metal center, no detailed electrochemical studies have been reported for such systems. Described herein is the detailed electrochemical investigation of the effect of ligand conformation on the redox properties of the corresponding Pd(II) complexes. These Pd complexes adopt different conformations in solution, as supported by studies using variable scan rate, variable-temperature cyclic voltammetry (CV), differential pulse voltammety, and digital CV simulations at variable scan rates. The effect of the axial amine protonation on the spectroscopic and electrochemical properties of the complexes was also investigated. A number of new Pd(III) complexes were characterized by electron paramagnetic resonance, UV-vis spectroscopy, and X-ray diffraction including [((tBu)N4)Pd(III)Cl2]ClO4, a dicationic [((tBu)N4)Pd(III)Me(MeCN)](OTf)2, and an unstable tricationic [((tBu)N4)Pd(III)(EtCN)2](3+) species. Although the electron-rich neutral complexes ((tBu)N4)PdMeCl and ((tBu)N4)PdMe2 are present in solution as a single isomer with the axial amines not interacting with the metal center, their low oxidation potentials are due to the presence of a minor conformer in which the (tBu)N4 ligand adopts a tridentade (κ(3)) conformation. In addition, the redox properties of the ((tBu)N4)Pd complexes show a significant temperature dependence, as the low-temperature behavior is mainly due to the contribution from the major, most stable conformer, while the room-temperature redox properties are due to the formation of the minor, more easily oxidized conformer(s) with the (tBu)N4 ligand acting as a tridentate (κ(3)) or tetradentate (κ(4)) ligand. Overall, the coordination to the metal center of each axial amine donor of the (tBu)N4 ligand leads to a lowering of the Pd(II/III) oxidation potential by ∼0.6 V. These detailed electrochemical studies can thus provide important insights into the design of new ligands that can promote Pd-catalyzed oxidation reactions employing mild oxidants such as O2.

Intramolecular non-covalent interactions as a strategy towards controlled photoluminescence in copper(I) complexes

In this work, we describe a new strategy for designing photoluminescent Cu(I) complexes. At its core are simple cyclophane inspired N-donor ligands featuring intramolecular interactions between aromatic units within a single molecule. Variation of the steric bulk inflicted a change in intramolecular stacking distances that in turn affected the emission colour of copper(I) complexes tunable in a 0.5 eV range from green to red. As the interactions driving emission are confined to the single molecule, no intermolecular aggregation is required to enable photoluminescence in solution, pristine crystals, or solution-cast polymer films. A crystallographic study provides a link between the spatial proximity of the aromatic rings of the ligands (ranging from 3.349 to 3.731 A) and the enhancement of emission efficiency, which increases dramatically from 0.02 to 0.78 at 296 K as the ring spacing contracts. Photophysical and theoretical analyses confirm the involvement of intramolecular interactions in the formation of the emissive state and describe the observed phenomena at the molecular level.

Dynamic Phosphorescent Probe for Facile and Reversible Stress Sensing

Dynamic phosphorescent copper complex incorporated into the main chain of polyurethanes produces a facile and reversible response to tensile stress. In contrast to common deformation sensors, the applied stress does not lead to bond scission, or alters the phosphor structure. The suppression of dynamics responsible for the nonradiative relaxation is found to be the major pathway governing stress response. As a result, the response of dynamic phosphor described in this work is stress specific. Compared to initial unloaded state, a nearly twofold increase of photoluminescence intensity occurs in response to a 5-35 MPa stress applied to pristine metalated polymers or their blends with various polyurethanes. Finally, the dynamic sensor proves useful for mapping stress distribution patterns and tracking dynamic phenomena in polyurethanes using simple optical imaging techniques.