Pyridine Nickel Research Articles

Reducing the Photodegradation of Perovskite Quantum Dots to Enhance Photocatalysis in CO2 Reduction

Solution-processed perovskite quantum dots (QDs) have been intensively researched as next-generation photocatalysts owing to their outstanding optical properties. Even though the intrinsic physical properties of perovskite QDs have been significantly improved, the chemical stability of these materials remains questionable. Their low long-term chemical stability limits their commercial applicability in photocatalysis. In this study, we investigated the photodegradation mechanisms of perovskite QDs and their hybrids via photoluminescence (PL) by varying the excitation power and the ultraviolet (UV) exposure power. Defects in perovskite QDs and the interface between the perovskite QD and the co-catalyst influence the photo-stability of perovskite QDs. Consequently, we designed a stable perovskite QD film via an in-situ cross-linking reaction with amine-based silane materials. The surface ligand comprising 2,6-bis(N-pyrazolyl)pyridine nickel(II) bromide (Ni(ppy)) and 5-hexynoic acid improved the interface between the Ni co-catalyst and the perovskite QD. Then, ultrathin SiO2 was fabricated using 3-aminopropyltriethoxy silane (APTES) to harness the strong surface binding energy of the amine functional group of APTES with the perovskite QDs. The Ni co-catalyst content was further increased through Ni doping during purification using a short surface ligand (3-butynoic acid). As a result, stable perovskite QDs with rapid charge separation were successfully fabricated. Time-correlated single photon counting (TCSPC) PL study demonstrated that the modified perovskite QD film exhibited slow photodegradation owing to defect passivation and the enhanced interface between the Ni co-catalyst and the perovskite QD. This interface impeded the generation of hot carriers, which are a critical factor in photodegradation. Finally, a stable red perovskite QD was synthesized by applying the same strategy and the mixture between red and green QD/Ni(ppy)/SiO2 displayed an CO2 reduction capacity for CO (0.56 µmol/(g∙h)).

Molecular weight control of polyethylene waxes using a constrained imino‐cyclopenta[b]pyridyl‐nickel catalyst

ABSTRACTFive examples of nickel(II) bromide complexes bearing N,N‐imino‐cyclopenta[b]pyridines, [7‐(ArN)‐6,6‐Me2C8H5N]NiBr2 (Ar = 2,6‐Me2C6H3 (Ni1), 2,6‐Et2C6H3 (Ni2), 2,6‐i‐Pr2C6H3 (Ni3), 2,4,6‐Me3C6H2 (Ni4), 2,6‐Et2‐4‐MeC6H2 (Ni5)), have been prepared by the reaction of the corresponding ligand, L1–L5, with NiBr2(DME) (DME = 1,2‐dimethoxyethane). On crystallization from bench dichloromethane, Ni1 underwent adventitious reaction with water to give the aqua salt, [L1NiBr(OH2)3][Br] (Ni1'). The molecular structures of Ni1' and Ni3 have been structurally characterized, the latter revealing a bromide‐bridged dimer. On activation with either MMAO or Et2AlCl, Ni1, Ni2, Ni4, and Ni5, all exhibited high activities for ethylene polymerization (up to 3.88 × 106 g(PE) mol−1(Ni) h−1); the most sterically bulky Ni3 gave only low activity. Polyethylene waxes are a feature of the materials obtained which typically display low molecular weights (Mws), narrow Mw distributions and unsaturated vinyl and vinylene functionalities. Notably, the catalyst comprising Ni1/Et2AlCl produced polyethylene with the lowest Mw, 0.67 kg mol−1, which is less than any previously reported data for any class of cycloalkyl‐fused pyridine–nickel catalyst. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 3494–3505

Coordination Chemistry and Reactivity of Bis(aldimino)pyridine Nickel Complexes in Four Different Oxidation States

A series of nickel complexes with potentially redox active bis(aldimino)pyridine ligands [NNN] ([NNN] = 1,1′-(pyridine-2,6-diyl)bis(N-arylmethanimine), where aryl = 2,6-diisopropylphenyl, mesityl, 4-methoxyphenyl, 4-trifluoromethylphenyl, and 3,5-bis(trifluoromethyl)phenyl) were synthesized, and their properties and reactivities were investigated as a function of the overall oxidation state of the system. (Ni[NNN])2+ complexes of ligands featuring bulky electron-rich substituents (1a-Br2 and 1b-Br2, [NNN] = 1,1′-(pyridine-2,6-diyl)bis(N-(2,6-diisopropylphenyl)methanimine) and 1,1′-(pyridine-2,6-diyl)bis(N-mesitylmethanimine), respectively) demonstrated five electrochemical reduction events, the first three of which were quasi-reversible. In contrast, only two quasi-reversible reductions were observed for the less bulky and electron-deficient N-aryl substituents 4-(trifluoromethyl)phenyl and 3,5-bis(trifluoromethyl)phenyl. Chemical reduction of 1a-Br2 and 1b-Br2 with 1 equiv of KC8 or CoCp*2 forms (Ni[NNN])+ complexes of the general formula Ni[NNN]Br (2a-Br and 2b-Br). Structural, spectroscopic, and theoretical studies reveal that these complexes feature significant unpaired spin density on the metal, consistent with “nickel(I)” character. This behavior is in contrast with previously reported bis(ketimino)pyridine systems, in which at the (Ni[NNN])+ state the unpaired electron resided exclusively in the ligand. Further reduction forms a series of (Ni[NNN])0 complexes, in which all of the potentially tridentate [NNN] ligands bind via only one iminopyridine unit; the second arm is left unbound in most complexes. Variable temperature NMR spectroscopy demonstrates that bound and unbound arms exchange via a postulated tridentate intermediate. Electrochemical reduction, via three sequential one-electron reductions, of 1a-Br2 and 1b-Br2 in the presence of CO2/H+ forms an active catalyst for H2 evolution at a glassy-carbon electrode surface, again emphasizing the unique redox chemistry of the bulky bis(aldimino)pyridine nickel complexes.

Synthesis and reactivity in ethylene oligomerization by heteroscorpionate dibromonickel(II) complexes

Novel heteroscorpionate ligands were synthesized by a Peterson rearrangement during the reaction of 2-pyridinecarboxaldehyde (or 2-quinolinecarboxaldehyde) and 1,1-carbonyl-bis(pyrazoles). Nickel(II) dibromide reacts with these ligands in THF to give the heteroscorpionate dibromo complexes of general formula LNiBr2. Crystal structures of two full-sandwich heteroscorpionate Ni(II) complexes were determined. Preliminary studies of catalytic activity in ethylene oligomerization using different organoaluminum cocatalysts were performed. The addition of one equivalent of triphenylphosphine resulted in increased catalytic activity for most examples. The catalyst system of (2-[bis(3,5-dimethylpyrazol-1-yl)methyl]pyridine nickel(II) dibromide/Et2AlCl/PPh3 dimerized ethylene with an activity of 650g oligomer mol−1Nih−1 while the share of 1-butene in the mixture has reached 75%. Tris(3,5-dimethylpyrazol-1-yl)methyl nickel(II) dibromide, activated by Et2AlCl/PPh3 produced isobutylene (75% of the butene fraction).

SYNTHESIS, CHARACTERIZATION AND BIOLOGICAL ACTIVITY OF POLYMER NICKEL (II) COMPLEX

4-vinyl pyridine nickel complex containing polymerizable vinyl group, prepared by condensing (4:1 molar ratio) of 4-vinylpyridine with Nickel chloride, then polymerized with methyl methacrylate at 70 °C using AIBN as initiator. Metal complexand polymer metal complex have been characterized by elemental analyses, molar conductance, IR, 1H-NMR , Massspectra and thermal analyses (DTA and TGA). Conductivity measurement reveals the nonelectrolytic nature of thecomplex. This confirms that, the anion is coordinated to the metal ion. The IR reveal the metal ion is coordinated via thenitrogen atom of 4-VP. Nickel complex and polymer nickel complex have been tested invitro against number of tumor andnumber of microorganisms in order to assess their anti tumor and antimicrobial properties. The antimicrobial activity wasobserved by compounds VP-Ni and MMA-VP-Ni under the screening conditions. The activity against HCT-116 cells wasdetected for compound VP-Ni (with IC50 value 9.8±0.6 µg/ml), compared with reference standard (24.6±0.3 µg/ml) followedby MMA-VP-Ni (48.3±1.5). In conclusion, this study highlighted the synthesis of polymer nickel complex, and proved thepromising biological activity of the synthesized compounds.

Ethylene oligomerization studies by nickel(ii) complexes chelated by (amino)pyridine ligands: experimental and density functional theory studies

Reductions of imine compounds 2-methoxy-N-(1-(pyridin-2-yl)ethylidene)ethanamine (L1), 2-methoxy-N-((pyridin-2-yl)methylene)ethanamine (L2), N,N-diethyl-N-((pyridin-2-yl)methylene)ethane-1,2-diamine (L3) and 2-((pyridin-2-yl)methyleneamino)ethanol (L4) using NABH4 produced their corresponding amine analogues N-(2-methoxyethyl)-1-(pyridin-2-yl)ethanamine (L1a), 2-methoxy-N-((pyridin-2-yl)methyl)-ethanamine (L2a), N,N-diethyl-N-((pyridin-2-yl)methyl)ethane-1,2-diamine (L3a) and 2-((pyridin-2-yl)methylamino)ethanol (L4a) in good yields. Reactions of the (amino)pyridine ligands L1a–L4a with [NiBr2(DME)] afforded nickel(II) complexes, [NiBr2(L1a)2] (1), [NiBr2(L2a)2] (2), [NiBr2(L3a)2] (3) and [NiBr2(L4a)2] (4), respectively in quantitative yields. Molecular structures of complexes 2 and 4 confirmed the formation of the bis(chelated)nickel(II) complexes. Activation of complexes 1–4 with either EtAlCl2 or methylaluminoxane (MAO), produced active ethylene oligomerization catalysts to afford mostly ethylene dimers (C4), in addition to trimmers (C6) and tetramers (C8). Density functional theory studies provided valuable insight into the reactivity trends and influence of complex structure on the ethylene oligomerization reactions.

Synthesis and Evaluation of Arylimino Pyridine Nickel(II) Catalysts: Influence of Substituents on Polyethylene Structure

The asymmetric arylimino pyridine Ni(II) catalysts have been examined with different substituents including diisopropyl, diethyl, fluoro, and chloro groups.The influence of these substituents and variation of ethylene pressure on the catalytic activity, crystalline structure, as well as on thermal properties of polyethylene has been investigated. The result show that complexes with substituent alkyl groups, which provide the increased electron density on the metal center (o-diethyl and o-diisopropyl) exhibit higher activity, compared to those with electron acceptors substituents (o-fluoro and o-chloro). Досліджені асиметричні ариліміно піридин Ni(II) каталізатори з різними замісниками, включаючи диізопропіл-діетил-, флуоро- і хлор-замісники. Досліджено вплив цих замісників і тиску етилену на каталітичну активність, кристалічну структуру, і термічні властивості поліетилену. Показано, що комплекси із заміщеними алкільними групами, які забезпечують підвищену електронну щільність на центрі металу (о-діетил і о-діізопропіл), більш активні в порівнянні з комплексами з електрон-акцепторними замісниками (о-флуоро і о-хлор).

The aldimine effect in bis(imino)pyridine complexes: non-planar nickel(I) complexes of a bis(aldimino)pyridine ligand.

Reduction of bis(aldimino)pyridine nickel(II) dihalide forms a non-planar bis(aldimino)pyridine nickel(I) halide. Unlike the previously reported square-planar bis(ketimino)pyridine nickel chloride, for which the spin density was localized on the ligand, the present species demonstrate N(py)-Ni-X angles of 156°-162° and significant spin density at the metal inferred from EPR measurements and DFT calculations.

Formation of Cationic Intermediates upon the Activation of Bis(imino)pyridine Nickel Catalysts

The activation of bis(imino)pyridine nickel(II) dichloride complexes [LNiCl2] with methylalumoxane (MAO) and AlMe3/[CPh3][B(C6F5)4] was studied by multinuclear NMR spectroscopy. Formation of similar outer-sphere ion pairs of the types [LNiMe]+[MeMAO]− and [LNiMe]+[B(C6F5)4]−, capable of promoting norbornene polymerization, was observed.

Substituent Effects of Pyridine-amine Nickel Catalyst Precursors on Ethylene Polymerization

A series of pyridine-amine nickel complexes with various substituents were synthesized and used to evaluate substituent effects of catalyst precursors on the reactivity of ethylene polymerization. Substituent effects, including the steric effect of the pyridine moiety, steric effect of the bridge carbon, and steric and electronic effects of the amine moiety, were investigated systematically. Introduction of bulky aryls onto the pyridine moiety on amine pyridine nickel leads to a significant decrease in the activity and molecular weight of polyethylene, whereas an increase in bulk of substituents on the bridge carbon causes an increase in the polymerization activity and molecular weight of polyethylene. For the amine moiety, increasing the steric hindrance results in decreasing activity and affords a higher molecular weight polyethylene with a narrower polydispersity, and introduction of an electron-donating group on the amine moiety leads to formation of a high molecular weight polyethylene with enhanced ...

Vinyl Polymerization of Norbornene on Nickel Complexes with Bis(imino)pyridine Ligands Containing Electron-Withdrawing Groups

A series of novel bis(imino)pyridine nickel(II) dichloride complexes, with the bis(imino)pyridine ligands containing electron-withdrawing groups (F, Cl, Br, CF3), have been prepared and characterized by elemental analysis and NMR spectroscopy. All complexes exhibit paramagnetically shifted 1H NMR spectra, indicative of the high-spin (S = 1) state of the d8 nickel(II) central atom. These complexes have been found to be highly active catalysts of vinyl-type norbornene polymerization upon activation with MAO, displaying activities up to 1.16 × 107 g of PNB (mol of cat.)−1 h–1 (the highest ever reported for norbornene polymerizations on bis(imino)pyridine nickel complexes) and yielding high-molecular-weight polynorbornene (Mw up to 4.5 × 106). X-ray structures for some of the nickel complexes are reported.

Nickel(II) Dibromide Complexes Bearing Bis(benzimidazolyl)amine and Bis(benzimidazolyl)pyridine Ligands for Ethylene Oligomerizations

A series of bis(benzimidazolyl)amine and bis(benzimidazolyl)pyridine ligands and their respective nickel(II) dibromide complexes were synthesized and fully characterized. After activation of the nickel complexes with ethylaluminum sesquichloride showed productivity in excess of 106 (g-oligomer)(mol-Ni)−1h−1bar−1 towards ethylene oligomerization, producing butenes as major products. The bis(benzimidazolyl)pyridine nickel complexes showed higher activity and dimerization selectivity than corresponding bis(benzimidazolyl)amine nickel complexes.

Bimetallic Nickel Aluminun Mediated Para-Selective Alkenylation of Pyridine: Direct Observation of η2,η1-Pyridine Ni(0)−Al(III) Intermediates Prior to C−H Bond Activation

We have presented new amino-NHC Ni-Al complex mediated para C-H bond activation for pyridine and quinolin, and isolated for the first time the intermediate structure of a bimetallic eta(2),eta(1)-pyridine nickel aluminum complex prior to its C-H activation, which serves as key evidence for bimetallic catalysis.

Synthesis, Crystal Structure, and Catalytic Performance of 2,6-Bis[1-(2,4,6-trimethylphenylimino)ethyl]pyridine Nickel(II) Complex

A novel nickel(II) complex Ni[L]Cl2CH3CN(1) containing the tridentate ligand 2,6-bis[1-(2,4,6-trimethylphenylimino)ethyl]pyridine(L) has been synthesized. The crystal structure of complex 1 was determined by single crystal X-ray diffraction analysis. The catalytic activity of complex 1 for the polymerization of ethylene was studied under activation with methylaluminoxane(MAO).

Olefin homopolymerization catalyzed over asymmetric and symmetric ni(II) diimine complexes

Symmetric and asymmetric Ni(II) diimine complexes such as 2-[(2,6-diisopropylphenylimino)methyl]pyridine nickel(II) dibromide (a), 2-[1-(2,6-diisopropylphenylimino)ethyl]pyridine nickel(II) dibromide (b) and [1,2-bis(2,6-diisopropylphenylimino)] acenaphthene nickel(II) dibromide (c) were synthesized. For olefin homopolymerization, asymmetric Ni(II) diimine complexes [(a) & (b)] were compared with symmetric system (c). Asymmetric Ni(II) diimine complexes exhibited less catalytic activity and thermal stability as well as more b-hydride elimination than a symmetric diimine complex (c). The activity of (a) was larger than that of (b), which indicates that methyl group has a contribution to the instability of catalyst by s bond vibration rather than the stabilization of the active site by electron releasing property.

Synthesis and Characterization of Poly(dihalophenylene oxide)s Through Bis(trihalophenolato)(ethylenediamine)(pyridine)nickel(II) Complexes in Solution in the Presence of Iodine

The thermal polymerization of bis(trihalophenolato)(ethylenediamine)(pyridine)Nickel(II) complexes in toluene, which were kept at different temperature (20–110°C) with different time intervals and different amounts of I2, have been studied. The characterization of the complexes were studied by using FTIR, UV-visible, DSC and elemental analysis. The effects of time, temperature, and the amount of iodine were investigated on the percent conversion, the structure, and molecular weights of the synthesized polymers. The characterization of the polymers were performed by FTIR, 1H NMR and 13C NMR spectroscopies, DSC, and viscometric measurements. All polymers are highly rigid. The optimum condition to obtain highest percent yield from the decomposition of these complexes in solution was: 50°C, 3 h polymerization time and 75% I2 for bis(2,4,6-trichlorophenolato)(ethylenediamine)(pyridine)nickel(II) complex, 110°C, 3 h polymerization time and 30% I2 for bis(2,4,6-tribromophenolato)(ethylenediamine)(pyridine)nickel(II) complex. 2,4,6-Trichlorophenolate, with the chelating and non-chelating ligands, displays selectively in favor of 1,2-catenation, whereas 1,2- and 1,4-catenation takes place at equal rates in the case of 2,4,6-tribromophenolate.

Crystal structure of a 1∶2∶1 packing complex formed by bis(isothiocyanato) tetrakis(pyridine) nickel(II), triphenylmethane, and metanol

The structure of the [NiPy4(NCS)2]·2(C6H5)3CH·CH3OH (Py is pyridine) packing complex was determined by single crystal X-ray diffraction analysis (KM-4 diffractometer, λMoKα, graphite monochromator, ω/2ϑ scan mode, θmax, 2073 reflections, R=0.059). The unit cell is base-centered monoclinic, space group C2/c, a=20.22(1), b=14.256(7), c=18.836(6) A, β=87.40(4)°, Z=4C61H56N6NiOS2, dcalc=1.239 g/cm3. The structure is of the island type and consists of molecules of three types. In the trans-[NiPy4(NCS)2] molecule, the central atom has a distorted octahedral environment and is coordinated by six nitrogen atoms of two isothiocyanate and four pyridine ligands. In contrast to the phase of the complex itself, this molecule acquires a four-lobe propeller conformation, in which the pyridine rings are rotated relative to the equatorial plane by angles of 52.8(3) and 50.1(2)°. The triphenylmethane molecule has a three-lobe propeller conformation, as in triphenylmethane clathrates with benzene, thiophene, pyrrole, and aniline, but strongly deviates from threefold axis symmetry. The phenyl rings form dihedral angles of 25(3), 40(4), and 19(4)° with the planes formed by the bonds of the ternary carbon atoms with hydrogen atoms and by the appropriate carbon atom of the phenyl ring. The methanol molecules are located inside the direct channels running along the c axis and are disordered around the inversion centers.

Crystal structure of the dinitratotetrakis(pyridine)nickel(II) clathrate with pyridine as guest, [NiPy4(NO3)2]·2Py

The structure of the [NiPy4(NO3)2]·2Py clathrate was determined by single crystal X-ray diffraction analysis (KM-4 diffractometer, λMoKa radiation, graphite monochromator, ω/2θ scan mode, θmax=30°, 640 reflections, R=0.065). Orthorthombic base-centered unit cell, space group Ccca, a=12.148(5), b=15.019(4), c=16.96(1) A, Z=4C30H30N8NiO6, dcalc=1.411 g/cm3. The structure is of island type and consists of distorted octahedral trans-[NiPy4(NO3)2] (host) and pyridine (guest) molecules. The Ni(II) cation coordinated by four nitrogens of the pyridine ligands and two oxygens of the nitrato groups lies in the special position 222; the twofold axes coincide with the directions of the metal-ligand bonds. The guest pyridine molecules lie on the twofold axes that are parallel to the c axes and are oriented in such a way that the total dipole moment of the guest subsystem is zero.

Preparation and x-ray crystal structure of deprotonated S-methyl-β-N-(pyridine N-oxide-2-ylmethylidene)dithiocarbazate pyridine nickel(II) perchlorate: [Ni(C 8H 8N 3OS 2)(C 5H 5N)]ClO 4

A nickel(II) complex with S-methyl-β-N-(pyridine N-oxide-2-ylmethylidene) dithiocarbazate (LH) and pyridine (Py) as ligands with the formula [NiLPy]ClO 4 has been synthesized. The crystal structure has been determined by X-ray diffraction analysis. Sulphur, nitrogen and oxygen atoms of the tridentate ligand, as well as a nitrogen atom of one additive pyridine, adopt a planar conformation to produce the square planar geometry at each nickel atom. Magnetic susceptibility and IR spectra are interpreted in accordance with the proposed stereochemistry.

Synthesis of n,n′‐biquinolines by a coupling reaction of bromoquinolines using organonickel(0) complexes

AbstractTris(triphenylphosphine)nickel(0) (A) and a zerovalent pyridine–nickel complex (B) have been used as reagents for the coupling reaction of 3‐, 6‐ and 8‐bromoquinolines: 3,3′‐, 6‐6′‐ and 8,8′‐ Biquinolines were obtained in quantitative yields when A was used as the coupling reagent. B gave always a mixture of the n,n′ ‐biquinoline and substitution products. A mechanism can be outlined to explain the coupling reaction of bromoquinolines using zerovalent nickel complexes.