Dinuclear gold(I) complexes based on carbene and diphosphane ligands: bis[2-(dicyclohexylphosphano)ethyl]amine complex inhibits the proteasome activity, decreases stem cell markers and spheroid viability in lung cancer cells.

Three new dinuclear gold(I) complexes (1-3) containing a carbene (1,3-Bis(2,6-di-isopropylphenyl)imidazol-2-ylidene (IPr)) and diphosphane ligands [bis(1,2-diphenylphosphano)ethane (Dppe), bis(1,3-diphenylphosphano)propane (Dppp) and bis[2-(dicyclohexylphosphano)ethyl]amine (DCyPA)], were synthesized and characterized by elemental analysis and, ESI-MS, mid FT-IR and NMR spectroscopic methods. The structures of complexes 2 and 3 were determined by X-ray crystallography, which revealed that the complexes are dinuclear having gold(I) ions linearly coordinated. The anticancer activities of the complexes (1-3) were evaluated in lung (A549), breast (MC-F7), prostate (PC-3), osteosarcoma (MG-63) and ovarian (A2780 and A2780cis) cancer models. Growth inhibition by the new complexes was higher than cisplatin in all cell lines tested. The mechanism of action of complex 3 was investigated in A549 cells using 2-dimensional (2D) models and 3D-multicellular tumor spheroids. Treatment of A549 cells with complex 3 caused: the induction of apoptosis and the generation of reactive oxygen species; the cell cycle arrest in the G0/G1 phase; the inhibition of both the proteasome and the NF-kB activity; the down-regulation of lung cancer stem cell markers (NOTCH1, CD133, ALDH1 and CD44). Complex 3 was more active than cisplatin also in 3D models of A549 lung cancer cells.

Unveiling meta-Alkyloxy/-Silyloxy-Substituted N-Aryl PNP Ligands for Efficient Cr-Catalyzed Ethylene Tetramerization.

Novel N-aryl-functionalized PNP ligands (1-4) bearing m-alkyloxy/-silyloxy substituents were prepared and evaluated for chromium-catalyzed ethylene oligomerization using MMAO-3A as an activator. The selected Cr/PNP system under optimized condition exhibited high 1-octene-selective (up to 70 wt %) ethylene tetramerization at a remarkable rate (over 3000 kg gCr-1 h-1). More importantly, the undesirable polyethylene selectivity was restricted to a minimum level of ∼1-2 wt % for pre-catalysts derived with ligands 1 and 2. Employing chlorobenzene as a reaction medium yielded best productivity in conjunction to the total α-olefin (1-C6 + 1-C8) selectivity (∼88 wt %). N-aryl PNP ligands (3 and 4) incorporating m-silyloxy substituents in the phenyl ring exhibited relatively poorer tetramerization performance while yielding higher PE fraction as compared to their m-alkyloxy derivatives. A detailed molecular structure of the best-performing pre-catalyst 1-Cr was established by single-crystal X-ray diffraction analysis. The stability of 1/Cr-based catalyst system was investigated for a reaction time of up to 2 h under optimized condition.

Highly Efficient Ethylene Tetramerization Using Cr Catalysts Constructed with Trifluoromethyl-Substituted N-Aryl PNP Ligands.

Tetramerization of ethylene by chromium catalysts stabilized with functionalized N-aryl phosphineamine ligands C6H4(m-CF3)N(PPh2)2 (1), C6H4(p-CF3)N(PPh2)2 (2), C6H4(o-CF3)N=PPh2-PPh2 (3), and C6H3(3,5-bis(CF3))N(PPh2)2 (4) was evaluated. The parameter optimization includes temperature, co-catalyst, and solvent. Upon activation with MMAO-3A, the new catalyst system especially with m-functional PNP ligand (1) exhibited high 1-octene selectivity and productivity while giving minimum undesirable polyethylene and C10 + olefin by-products. Using PhCl as a solvent at 75 °C led to a remarkable α-olefin (1-C6 + 1-C8) selectivity (>90 wt %) at a reaction rate of 2000 kg·gCr -1·h-1. Under identical conditions, analogous PNP ligands bearing -CH3, -Et, and -Cl functional moieties at the meta position of the N-phenyl ring displayed significantly lower reactivity. The catalyst with p-functional ligand (2) exhibited lower activity and comparable selectivities, while the Cr/PPN (with ligand 3) system gave no noticeable reactivity. The molecular structure of the precatalyst (1-Cr), exhibiting a monomeric structural feature, was elucidated with the aid of single-crystal X-ray diffraction study.

Mixed-Metal Cu-BTC Metal-Organic Frameworks as a Strong Adsorbent for Molecular Hydrogen at Low Temperatures.

The advancement of hydrogen and fuel cell technologies hinges on the development of hydrogen storage methods. Metal-organic frameworks (MOFs) are one of the most favorable materials for hydrogen storage. In this study, we synthesized a series of isostructural mixed-metal metal-organic frameworks (MM-MOFs) of 1,3,5-benzenetricarboxylate (BTC), M-Cu-BTC, where M = Zn2+, Ni2+, Co2+, and Fe2+ using the post-synthetic exchange (PSE) method with metal ions. The powder X-ray diffraction patterns of MM-MOFs were similar with those of single-metal Cu-BTC. Scanning electron microscopy indicates the absence of amorphous phases. Inductively coupled plasma mass spectroscopy of the MM-MOFs shows successful metal exchanges using the PSE method. The N2 adsorption measurements confirmed the successful synthesis of porous MM-MOFs. The metal exchanged materials Ni-Cu-BTC, Zn-Cu-BTC, Fe-Cu-BTC, and Co-Cu-BTC were studied for hydrogen storage and showed a gravimetric uptake of 1.6, 1.63, 1.63, and 1.12 wt %; respectively. The increase in hydrogen adsorption capacity for the three metal exchanged materials is about 60% relative to that of the parent MOF (Cu-BTC). The improvement of gravimetric uptake in M-Cu-BTC (where M = Ni2+, Zn2+, and Fe2+) is probably due to the increase in binding enthalpy of H2 with the unsaturated metal sites after the partial exchange from Cu2+ to other metal ions. The higher charge density of metal ions strongly polarizes hydrogen and provides the primary binding sites inside the pores of Cu-BTC and subsequently enhances the gravimetric uptake of hydrogen.

Near-White Light Emission from Lead(II) Metal-Organic Frameworks.

Reaction of bpy (bpy = 4,4'-bipyridine) with Pb(OAc)2·3H2O in DMF (DMF = dimethylformamide) afforded a metal-organic framework (MOF), [Pb2(µ-bpy)(µ-O2CCH3)2(µ-O2CCH3)2]·H2O (1). Reaction of bpy with Pb(O2CCF3)2 in a methanol and chloroform mixture furnished another MOF, [Pb(µ-bpy)(µ-O2CCF3)2]·1/2CHCl3 (2). However, the reaction of bpy with Pb(OAc)2·3H2O in the presence of trifluoroacetic acid in a similar reaction condition yielded a hydrogen-bonded zwitter-ionic complex of Pb(II), [Pb(bpy-H)2(O2CCF3)4] (3). All compounds have been characterized by single crystal X-ray crystallography, FT-IR, and 1H NMR spectroscopies. Compound 1 forms four heptacoordinated Pb(II) joined by (OCCH3)-O- linkages, resulting in a 3D noninterpenetrated MOF net with a four-connected uninodal sra (SrAl2) topology. However, in 2, tetra-connected Pb4(O2CCF3)8 cluster units are linked further through eight bpy ligands to furnish a doubly interpenetrated MOF with a new topology but having the very similar connectivity of 1, whereas 3 forms a zigzag hydrogen-bonded chain structure. The variation of carboxylate anions, pH of the reaction medium, and the ratio of the reactants profoundly affected the final topological structure of the compounds synthesized. The solid-state photoluminescence of 1-3 was investigated at room temperature. Interestingly 1, 2, and 3 achieved close to white light emission when excited at 329, 376, and 330 nm, respectively. The systematic understanding of the photophysical properties of analogous Pb-based compounds may open new perspectives for developing single-phase white-light-emitting materials using Pb(II) based MOFs.

Quest for highly connected metal-organic framework platforms: rare-earth polynuclear clusters versatility meets net topology needs.

Gaining control over the assembly of highly porous rare-earth (RE) based metal-organic frameworks (MOFs) remains challenging. Here we report the latest discoveries on our continuous quest for highly connected nets. The topological exploration based on the noncompatibility of a 12-connected RE polynuclear carboxylate-based cluster, points of extension matching the 12 vertices of the cuboctahedron (cuo), with 3-connected organic ligands led to the discovery of two fascinating and highly connected minimal edge-transitive nets, pek and aea. The reduced symmetry of the employed triangular tricarboxylate ligand, as compared to the prototype highly symmetrical 1,3,5-benzene(tris)benzoic acid guided the concurrent occurrence of nonanuclear [RE9(µ3-OH)12(µ3-O)2(O2C-)12] and hexanuclear [RE6(OH)8(O2C-)8] carboxylate-based clusters as 12-connected and 8-connected molecular building blocks in the structure of a 3-periodic pek-MOF based on a novel (3,8,12)-c trinodal net. The use of a tricarboxylate ligand with modified angles between carboxylate moieties led to the formation of a second MOF containing solely nonanuclear clusters and exhibiting once more a novel and a highly connected (3,12,12)-c trinodal net with aea topology. Notably, it is the first time that RE-MOFs with double six-membered ring (d6R) secondary building units are isolated, representing therefore a critical step forward toward the design of novel and highly coordinated materials using the supermolecular building layer approach while considering the d6Rs as building pillars. Lastly, the potential of these new MOFs for gas separation/storage was investigated by performing gas adsorption studies of various probe gas molecules over a wide range of pressures. Noticeably, pek-MOF-1 showed excellent volumetric CO2 and CH4 uptakes at high pressures.