Single and double deprotonation/dearomatization of the N,S-donor pyridinophane ligand in ruthenium complexes.

We report a series of ruthenium complexes with a tetradentate N,S-donor ligand, 2,11-dithia[3.3](2,6)pyridinophane (N2S2), that undergo single and double deprotonation in the presence of a base leading to the deprotonation of one or both pyridine rings. Both singly and doubly deprotonated complexes were structurally characterized by single-crystal X-ray diffraction. The NMR spectra are indicative of the dearomatization of one or both pyridine rings upon the deprotonation of the CH2-S arm, similar to the dearomatization of phosphine-containing pincer ligands. The deprotonated (N2S2)Ru complexes did not show appreciable catalytic or stoichiometric reactivity in transfer hydrogenation, hydrogenation and dehydrogenation of alcohols, and attempted activation of H2, CO2, and other substrates. Such a lack of reactivity is likely due to the low stability of the deprotonated species as evident from the structural characterization of one of the decomposition products in which shrinkage of the macrocyclic ring occurs via picolyl arm migration.

Ethylene binding in mono- and binuclear CuI complexes with tetradentate pyridinophane ligands.

Herein we report a series of CuI complexes supported by tetradentate RN4 pyridinophane ligands that coordinate to ethylene forming either mononuclear complexes with ethylene coordinated in an η2-mode or a binuclear complex where ethylene binds to two Cu atoms in a µ-η2-η2-mode, depending on the steric effects of the RN4 ligand and the reaction conditions. In the binuclear complex with bridging ethylene, the CC bond is significantly elongated, with a bond length of 1.444(8) Å according to X-ray diffraction analysis. This complex represents the only examination a µ-η2-η2-coordinated Cu-olefin complex reported to date, featuring one of the longest reported CC bonds. The spectroscopic characterization, structure, electrochemical properties and solution behavior are analyzed in this study. Coordination of ethylene was found to be reversible in these complexes and more favored in less sterically hindered RN4 ligands, so that ethylene binding is observed in a coordinating solvent (MeCN) environment. In the case of the MeN4 ligand, the ethylene complex is photoluminescent in the solid state. The ethylene binding modes in mono- and binuclear complexes are elucidated through Natural Bond Orbital and QTAIM analyses.

Triboluminescence of a new family of CuI-NHC complexes in crystalline solid and in amorphous polymer films.

Triboluminescent compounds that generate emission of light in response to mechanical stimulus are promising targets in the development of "smart materials" and damage sensors. Among triboluminescent metal complexes, rare-earth europium and terbium complexes are most widely used, while there is no systematic data on more readily available and inexpensive Cu complexes. We report a new family of photoluminescent Cu-NHC complexes that show bright triboluminescence (TL) in the crystal state visible in ambient indoor light under air. Moreover, when these complexes are blended into amorphous polymer films even at small concentrations, TL is easily observed. Observation of TL in polymer films overcomes the limitation of using crystals and opens up possibilities for the development of mechanoresponsive coatings and materials based on inexpensive metals such as Cu. Our results may also have implications for the understanding of the TL effect's origin in polymer films.

Highly sensitive mechano-controlled luminescence in polymer films modified by dynamic CuI-based cross-linkers.

Dynamic CuI-based mechanophores used as cross-linkers in polybutylacrylates enable highly sensitive detection of mechanical stress even at small strain (<50%) and stress (<0.1 MPa) values via reversible changes in luminescence intensity. Such sensitivity is superior to previously reported systems based on classical organic mechanophores and it allows for direct visualization of mechanical stress by imaging methods.

Facile and reversible double dearomatization of pyridines in non-phosphine MnI complexes with N,S-donor pyridinophane ligand.

Single and double dearomatization of pyridine rings was observed in MnI complexes with an N2S2 pyridinophane ligand via deprotonation of one or two CH2 arms, respectively. In contrast to other N,S-donor pincer-like systems, the dearomatized (N2S2)Mn species were found to be stable, with the dearomatization being reversible.

Interplay between the Conformational Flexibility and Photoluminescent Properties of Mononuclear Pyridinophanecopper(I) Complexes.

The macrocyclic ligand conformational behavior in solution, solid-state structures and the photophysical properties of copper(I) cationic and neutral mononuclear complexes supported by tetradentate N, N'-dialkyl-2,11-diaza[3.3](2,6)-pyridinophane ligands RN4 (R = H, Me, iBu, secBu, neoPent, iPr, Ts) were investigated in detail. Steric properties of the alkyl group at the axial amine in the RN4 ligand were found to strongly affect the conformational preferences and dynamic behavior in solution. Several types of conformational exchange processes were revealed by variable-temperature NMR and 2D exchange spectroscopy, including degenerative exchange in a pseudotetrahedral species as well as exchange between two isomers with different conformers of tri- and tetracoordinate RN4 ligands. These exchange processes are slower for the complexes containing bulky alkyl groups at the amine compared to less sterically demanding analogues. A clear correlation is also observed between the steric bulk of the alkyl substituents and the photoluminescent properties of the derived complexes, with less dynamic complexes bearing bulkier alkyl substituents exhibiting higher absolute photoluminescence quantum yield (PLQY) in solution and the solid state: PLQY in solution increases in the order Me < neoPent < iBu < secBu ≈ iPr < tBu. The electrochemical properties of the cationic complexes [(RN4)CuI(MeCN)]X (X = BF4, PF6) were also dependent on the steric properties of the amine substituent.