Photophysical Studies of a Zr(IV) Complex with Two Pyrrolide-Based Tetradentate Schiff Base Ligands

The reaction of two equivalents of N,N'-bis(2-pyrrolylmethylidene)-1,2-phenylenediamine (H2bppda) with tetrabenzylzirconium provided the air- and moisture-stable eight-coordinate complex Zr(bppda)2. Temperature-dependent steady-state and time-resolved emission spectroscopy established weak photoluminescence (ΦPL = 0.4% at 293 K) by a combination of prompt fluorescence and thermally activated delayed fluorescence (TADF) upon visible light excitation at and around room temperature. TADF emission is strongly quenched by 3O2 and shows highly temperature-sensitive emission lifetimes of hundreds of microseconds. The lifetime of the lowest energy singlet excited state, S1, was established by transient absorption spectroscopy and shows rapid deactivation (τ = 142 ps) by prompt fluorescence and intersystem crossing to the triplet state, T1. Time-dependent density functional theory (TD-DFT) calculations predict moderate ligand-to-metal charge transfer (LMCT) contributions of 25-30% for the S1 and T1 states. A comparison of Zr(bppda)2 to related zirconium pyridine dipyrrolide complexes, Zr(PDP)2, revealed important electronic structure changes due to the eight-coordinate ligand environment in Zr(bppda)2, which were correlated to differences in the photophysical properties between the two compound classes.

Applications of Cu(0) encapsulated nanocatalysts as superior catalytic systems in Cu-catalyzed organic transformations

Recently, Cu nanoparticles (NPs) encapsulated into various materials as supports (e.g., zeolite, silica) have attracted much devotion due to their unique catalytic properties such as high catalytic activity, intensive reactivity and selectivity through highly protective properties. Nowadays, the superior catalytic activity of Cu-NPs, encapsulated onto zeolite, silica and different porous systems, is extensively investigated and now well-established. As a matter of fact, Cu-NPs are protected from deactivation by this kind of encapsulation. Thus, their exclusion proceeds smoothly, and their recyclability is significantly increased. Cu-NPs have been used as potential heterogeneous catalysts in different chemical transformations. In this review, we try to show the preparation and applications of Cu(0) encapsulated nanocatalysts in zeolite and silica as superior catalytic systems in Cu-catalyzed organic transformations. In addition, the catalytic activity of these encapsulated Cu-NPs in different important organic transformations (such as hydrogenation, oxidation and carbon-carbon bond formations) are compared with those of a variety of organic, inorganic and hybrid porous bearing a traded metal ion. Moreover, the results from the TGA/DTA analysis and optical properties of Cu-complexes are demonstrated. The inherited characteristic merits of the encapsulated Cu-NPs onto zeolite and silica, such as their low leaching, catalytic activity, reusability economic feasibility and originality are critically considered.