Iridium(I)/N-Heterocyclic Carbene Hybrid Materials: Surface Stabilization of Low-Valent Iridium Species for High Catalytic Hydrogenation Performance

An Ir-I(NHC)-based hybrid material was prepared using a methodology which allowed the precise positioning and isolation of the Ir centers along the pore channels of a silica framework. The full characterization of the material by solid-state NMR spectroscopy showed that the supported Ir sites were stabilized by the silica surface, as low-coordinated single-site complexes. The material is extremely efficient for the hydrogenation of functional alkenes. The catalytic performance (TOF and TON) is one to two orders of magnitude higher than those of their molecular Ir analogues, and could be related to the prevention of the bimolecular deactivation of Ir complexes observed under homogeneous conditions

The case of a Cd2Cu2 complex containing an apparently C3-symmetric ligand : Erroneous ligand-structure assignment by X-ray diffraction data analysis

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Phosphine-based push-pull AIE fluorophores: Synthesis, photophysical properties, and TD-DFT studies

International audienceAbstract When periodically packing the intramolecular donor-acceptor structures to form ferroelectric-like lattice identified by second harmonic generation, our CD49 molecular crystal shows long-wavelength persistent photoluminescence peaked at 542 nm with the lifetime of 0.43 s, in addition to the short-wavelength prompt photoluminescence peaked at 363 nm with the lifetime of 0.45 ns. Interestingly, the long-wavelength persistent photoluminescence demonstrates magnetic field effects, showing as crystalline intermolecular charge-transfer excitons with singlet spin characteristics formed within ferroelectric-like lattice based on internal minority/majority carrier-balancing mechanism activated by isomer doping effects towards increasing electron-hole pairing probability. Our photoinduced Raman spectroscopy reveals the unusual slow relaxation of photoexcited lattice vibrations, indicating slow phonon effects occurring in ferroelectric-like lattice. Here, we show that crystalline intermolecular charge-transfer excitons are interacted with ferroelectric-like lattice, leading to exciton-lattice coupling within periodically packed intramolecular donor-acceptor structures to evolve ultralong-lived crystalline light-emitting states through slow phonon effects in ferroelectric light-emitting organic crystal

Unexpected Structure of a Helical N 4 -Schiff-Base Zn(II) Complex and Its Demetallation: Experimental and Theoretical Studies

International audienceA new Zn‐N4‐Schiff base L=((±)‐trans‐N,N’‐Bis(2‐aminobenzylidene)‐1,2‐diaminocyclohexane) complex was synthesized and fully characterized, showing an unexpected self‐assembled double‐stranded helicate structure. The X‐ray crystal analysis of the Zn2L2 complex ((C40H44N8Zn2,CH2Cl2, a=14.2375(3) Å, b=16.7976(4) Å, c=16.1613(4) Å, monoclinic, P21/n, Z=4) shows a centrosymmetrical structure in which zinc atoms are in distorted tetrahedral environments, revealing an M‐ (R, R) left‐handed helicity in its asymmetric unit. However, it was observed that this dinuclear complex is thermodynamically unstable in the presence of small water amounts and undergoes demetallation into free N4‐Schiff base ligand and ZnO nanoparticles. This hydrolysis process was thoroughly identified and monitored through detailed 1H NMR, DOSY NMR analysis. The reaction mechanism of this demetallation event was elucidated by using the DFT method, involving an activation energy smaller than 13 kcal/mol. Besides, a theoretical mechanism of the demetallation process is given for the first time

Sensitive 1,1-dicyanovinyl push-pull dye for primary amine sensing in solution by fluorescence

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Titanacalixarenes in Homogeneous Catalysis: Synthesis, Conformation and Catalytic Activity in Ethylene Polymerisation

International audienceVariously substituted titanacalixarenes were synthesised and tested for their performance as catalysts in ethylene polymerisation: p-tert-butylcalix[4]arene was derivatised to afford distal diether p-tert-butylcalix[4]arenes L1–L4, distal dihydroxy-depleted L5, proximal dihydroxy-depleted L6, proximal diether p-tert-butylcalix[4]arene L7, proximal intrabridged disiloxane L8 and proximal monoether L9. (Dichlorotitana)-p-tert-butylcalix[4]arenes 1–8 and (monochlorotitana)-p-tertbutylcalix[4]arene 9 have been successfully synthesised by reacting L1–L4 with TiCl4·2THF or L5–L9 with TiCl4. The structural conformation of complexes 1–9 in solution were determined by 1H NMR, 13C NMR, NOESY and COSY spectroscopic studies. Compounds 2, 3 and 4 have been structurally characterised by single-crystal X-ray diffraction. Upon activation with methylaluminoxane, compounds 1–8 revealed low to moderate activities for the production of high-density polyethylene (HDPE) to ultra-high-molecular-weight polyethylene (UHMWPE). 6/MAO gave the best activity at 770 kgPE (mol Ti)–1 h–1

Synthesis of novel tantalacalixarene complexes: first example of intramolecular CH activation of monodepleted aromatic ring

International audienceThe alkylation of (dichlorotantala)-p-tert-butylcalix[4]arenes 1 and 3 by two equivalents of NpMgCl (Np = neopentyl) affords the corresponding unreported (bisneopentyltantala)-p-tert-butylcalix[4]arenes 4 and S. These complexes can undergo dealkylation by modest increase of the temperature to yield 6 and 7. The characterization and structural conformation of the complexes 6 and 7 were determined by H-1, C-13, NOESY, and COSY spectroscopic studies and single-crystal X-ray diffraction. 7 exhibits unprecedented use of an intramolecular C H activation of an aromatic ring and simultaneously releases of one equivalent of neopentane. DFT calculation supports a mechanism in which the metal passes through a transition state involving a coplanar arrangement with its three ligands (C-Ar, H-Ar., C-Np)