Tongling Liang

Syntheses, Structures, and Fluorescent Properties of 2-(1H-Imidazol-2-yl)phenols and Their Neutral Zn(II) Complexes

A series of 2-(imidazole-2-yl)phenol ligands L1-L6 with the general composition 4-R(4)-5-R(3)-6-R(2)-2-(4,5-R(1),R(1)-1H-imidazole-2-yl)phenol (L1: R(1) = C(2)H(5), R(2) = R(3) = R(4) = H; L2: R(1) = C(6)H(5), R(2) = R(3) = R(4) = H; L3: R(1) = C(6)H(5), R(3) = OCH(3), R(2) = R(4) = H; L4: R(1) = C(6)H(5), R(4) = OCH(3), R(2) = R(3) = H; L5: R(1) = C(6)H(5), R(3) = H, R(2) = R(4) = CH(3); L6: R(1) = C(6)H(5), R(3) = H, R(2) = R(4) = t-Bu) and L7 (2,4-di-tert-butyl-6-(1H-phenanthro[9,10-d]imidazol-2-yl)phenol) and their neutral Zn(II) complexes (Z1-Z7) were synthesized and characterized by spectroscopic and elemental analyses. Molecular structures of L1, L5, Z1, and Z2 were confirmed by single-crystal X-ray diffraction. L1 crystallized in the monoclinic Cc space group, while L5, Z1, and Z2 all crystallized in the triclinic P1 space group. One-dimensional arrays based on continuous pi-pi stacking interactions and hydrogen bonding were observed for L1 and Z1, while L5 existed as discrete dimeric stack units. Z2 formed hydrogen-bonded 1D network structures but was completely devoid of pi-pi stacking interactions. Emission processes were found to be more dependent on the substituents on phenol as well as condensed media. In contrast to general conclusions on closely related systems in the literature, significant photorelaxation from the excited enol state was observed in the cases of L1 in methanol and L4 in both THF and methanol. Therefore, there exists a certain unusual hindering factor to keto-enol phototautomerism in the ligand-solvent systems. The sensing property of zinc(II) complexes was explored regarding the effects of substituents in their ligands. It was observed that coordination to the zinc(II) ion led to emission quenching for L1 and L2 while causing an enhancement of fluorescent intensity for L3, L4, L5, and L6. A linear relationship was observed between the emission intensity and the concentration of the zinc ion at the 10(-8) M level. Compared to other zinc compounds in this work, fluorescence enhancement in Z3 and Z4 showed that the methoxyl substituent is favorable for fluorescent enhancement.

2-[1-(2,4-Dibenzhydryl-6-methylphenylimino)ethyl]-6-[1-(arylimino)ethyl]pyridylcobalt(II) dichlorides: Synthesis, characterization and ethylene polymerization behavior

A series of cobalt(II) dichloride complexes ligated by 2-[1-(2,4-dibenzhydryl-6-methylphenylimino) ethyl]-6-[1-(arylimino)ethyl]pyridines was synthesized and characterized by FT-IR spectroscopy and elemental analysis. The molecular structure of the representative complex Co4 (R1 = Me, R2 = Me) was confirmed as pseudo square-pyramidal geometry at cobalt by single-crystal X-ray diffraction. Upon treatment with the co-catalysts MAO or MMAO, all cobalt pre-catalysts exhibited high activities up to 1.81 × 107 g PE mol−1(Co) h−1 in ethylene polymerization, and produced polyethylene products with molecular weights in the tens of thousands and narrow molecular weight distributions. The influence of the reaction parameters and nature of the ligands on the catalytic behavior of the title cobalt complexes was investigated.

Synthesis, characterization and ethylene oligomerization behaviour of 8-(1-aryliminoethylidene)quinaldinylnickel dihalides

A series of 8-(1-aryliminoethylidene)quinaldines and the nickel halides thereof were synthesized and characterized, and the molecular structures of two representative nickel complexes were confirmed by single-crystal X-ray diffraction studies. Upon treatment with diethylaluminium chloride (Et2AlCl), the nickel pro-catalysts exhibited high activity for ethylene oligomerization (1.24–1.83 × 106 g mol−1(Ni) h−1) with good thermal stability at 60 °C under 10 atm of ethylene. The influence of the reaction parameters on the catalytic behaviour was investigated for these nickel-based systems, including variation of Al/Ni molar ratio and reaction temperature. Furthermore, the effect of the ancillary ligand Ph3P was also probed.

8-(2-Cycloalkylphenylimino)-5,6,7-trihydro-quinolylnickel halides: polymerizing ethylene to highly branched and lower molecular weight polyethylenes

Cycloalkyl-modified 8-arylimino-5,6,7-trihydroquinolylnickel pre-catalysts, activated with either MAO or Et2AlCl, are highly active for the polymerization of ethylene into branched polyethylene waxes with narrow polydispersity.

Targeting polyethylene waxes: 9-(2-cycloalkylphenylimino)-5,6,7,8-tetrahydrocycloheptapyridylnickel halides and their use as catalysts for ethylene polymerization

A series of 9-(2-cycloalkylphenylimino)-5,6,7,8-tetrahydrocycloheptapyridine derivatives (L1–L3) was synthesized, and reacted with nickel halides to form their corresponding nickel complexes (bromide: Ni1–Ni3; chloride: Ni4–Ni6). All organic compounds and nickel complexes were well characterized. The structure of a representative complex Ni1 was determined by a single crystal X-ray study, revealing a distorted trigonal bipyramidal geometry at the nickel centre. Upon activation with either modified methylaluminoxane (MMAO) or diethylaluminium chloride (Et2AlCl), all nickel complexes showed high activities toward ethylene polymerization. The obtained polymers were confirmed to be polyethylene waxes with low molecular weights (in the range of 1.83 to 6.78 kg mol−1) and narrow polydispersity (PDI: 1.38–1.78); moreover, the obtained polyethylenes were highly branched ones. These polyethylene waxes have potential application as functional adducts of lubricants or pour-point depressants.

Controlling the molecular weights of polyethylene waxes using the highly active precatalysts of 2-(1-aryliminoethyl)-9-arylimino-5,6,7,8-tetrahydrocycloheptapyridylcobalt chlorides: synthesis, characterization, and catalytic behavior

A series of 2-(1-aryliminoethyl)-9-arylimino-5,6,7,8-tetrahydrocycloheptapyridylcobalt chlorides were synthesized and characterized using FT-IR and elemental analysis, and the molecular structures of complexes , and were confirmed to present a pseudo-square-pyramidal or trigonal-bipyramidal geometry around the cobalt center using single-crystal X-ray diffraction. Upon activation with either methylaluminoxane (MAO) or modified methylaluminoxane (MMAO), all cobalt precatalysts gave high activities up to the level of 10(7) gPE mol(-1) (Co) h(-1) toward ethylene polymerization, being one of most active cobalt-based precatalysts. In comparison with cobalt analogues, the title precatalysts generally possessed longer lifetime along with good thermo-stability; moreover, the resultant polyethylenes were highly linear and unimodal in most cases.

Rigid geometry 8-arylimino-7,7-dimethyl-5,6-dihydroquinolyl nickel bromides: single-site active species towards ethylene polymerization

The fused ring heterocyclic ketone, 5,6-dihydro-7,7-dimethylquinolin-8-one, was prepared and employed for the synthesis of a series of 8-arylimino-7,7-dimethyl-5,6-dihydroquinoline derivatives (aryl = 2,6-Me2Ph (L1), 2,6-Et2Ph (L2), 2,4,6-Me3Ph (L3), 2,6-Et2-4-MePh (L4), 2,6-i-Pr2Ph (L5)). The reaction of L1–L4 with (DME)NiBr2 (DME = 1,2-dimethoxyethane) gave the corresponding cationic bis-chelates, [(Lx)2NiBr][Br] (Lx = L1 (Ni1), L2 (Ni2), L3 (Ni3), L4 (Ni4)), as bromide salts; no such complex could be isolated with the most sterically bulky L5. All new compounds were characterized using IR spectroscopy, elemental analysis and in the case of L1–L5 using 1H and 13C NMR spectroscopy. Furthermore, the molecular structures of Ni1 and Ni3 have been determined and they reveal cation–anion pairs based on a trigonal bipyramidal nickel-containing cation charge balanced by a bromide counterion. In addition, X-ray photoelectron spectroscopy (XPS) was used to probe the solid state structures of L1, L3 and Ni1–Ni4; this technique provided valuable information regarding the net charge on nickel within the complexes. Upon activation with either methylaluminoxane (MAO) or ethylaluminium sesquichloride (EASC), all nickel complexes exhibited high activities towards ethylene polymerization and produced polyethylene waxes with low molecular weights. The catalytic activities, Ni1 [2,6-di(Me)] > Ni3 [2,4,6-tri(Me)] > Ni4 [2,6-di(Et)-4-Me] > Ni2 [2,6-di(Et)], correlated well with the trend in net charges observed in XPS analysis. The polydispersities (1.7–2.0) obtained for polyethylenes are narrow and indicate genuinely single-site active species for these catalysts. These performance characteristics have been attributed to the influence of the rigid geometry imparted by L1–L5 that, due to the presence of 7,7-dimethyl-substituents, prevents imine–enamine tautomerization.

Ultra-high molecular weight elastomeric polyethylene using an electronically and sterically enhanced nickel catalyst

A collection of ten related 1,2-bis(imino)acenaphthene-nickel(II) halide complexes, [1-[2,6-{(C6H5)2CH}2-4-{C(CH3)3}-C6H2N]-2-(ArN)C2C10H6]NiX2 (X = Br: Ar = 2,6-Me2C6H3Ni1, 2,6-Et2C6H3Ni2, 2,6-iPr2C6H3Ni3, 2,4,6-Me3C6H2Ni4, 2,6-Et2-4-MeC6H2Ni5) and (X = Cl: Ar = 2,6-Me2C6H3Ni6, 2,6-Et2C6H3Ni7, 2,6-iPr2C6H3Ni8, 2,4,6-Me3C6H2Ni9, 2,6-Et2-4-MeC6H2Ni10), each bearing one sterically and electronically enhanced N-2,6-dibenzhydryl-4-t-butylphenyl group, have been prepared and fully characterized. The unsymmetrical nature of the chelating bis(imino)acenaphthene is confirmed in the paramagnetic 1H NMR spectra for Ni1–Ni10, while the molecular structures of Ni1, Ni2 and Ni6 highlight the unequal steric protection of the nickel center imposed by their respective N,N-ligands. On activation with either Et2AlCl or MMAO, all the nickel complexes were highly active catalysts in ethylene polymerization [as high as 1.26 × 107 g of PE per mol of Ni per h] affording exceptionally high molecular weight (up to 3.1 × 106 g mol−1) hyper-branched polyethylene. Analysis of the mechanical properties reveals the ultra-high molecular weight polymers possess high tensile strength, excellent shape fixity and elastic recovery (up to 69%) as well as high elongation at break (eb = 843.9%); such materials offer a promising alternative to current thermoplastic elastomers (TPEs).

Sodium iminoquinolates with cubic and hexagonal prismatic motifs: synthesis, characterization and their catalytic behavior toward the ROP of rac-lactide

A series of sodium 2-arylimino-8-quinolates, C1–C8, differing in both the nature of the aryl and quinolate substituents, was prepared and characterized by 1H/13C NMR spectroscopy and elemental analysis. Their X-ray structures reveal multimetallic assemblies adopting a variety of structural cores all based on Na–O repeat units: cubic and tetrametallic for C1, C2 and C4, hexagonal prismatic and hexametallic for C3 and C5, and for tetrametallic C7′ a core resembling a cyclooctatetraene-type tub-shape. In the presence of BnOH, C1–C8 exhibit good activities towards the ring-opening polymerization (ROP) of rac-lactide, affording amorphous polylactides with broad molecular weight distributions. Furthermore, the substituent variation within the ligand frame of C1–C8 affects the catalytic activities of the ROP with the least sterically hindered system, C1, yielding the highest conversion. Introduction to the international collaboration The international collaboration between Professor Wen-Hua Sun at the Institute of Chemistry, Chinese Academy of Sciences (CAS) and Dr Gregory A. Solan at the University of Leicester, UK started in 2014 through a combination of shared scientific interests and common research goals. To strengthen this collaboration Dr Solan was awarded a CAS Presidents International Fellowship for Visiting Scientists in 2015. This scheme supports highly-qualified international scientists to carry out cooperative projects at CAS-affiliated institutions for 1–12 months and covers daily living expenses and international travel costs. The fellowship also aims to strengthen partnerships between CAS host institutions and the recipients’ home institution. Dr Solan, having first visited the Institute of Chemistry, CAS in Beijing in 2012, has been able to make a more extended 3 month stay during his sabbatical leave in 2016 working in Professor Suns laboratory for synthesizing a range of important polymeric materials including polyethylenes and polyesters.

Enhancing catalytic activity towards Heck-reaction by using 4,5,9,10-tetra(arylimino)pyrenylidenyldipalladium tetrachlorides

A series of binuclear 4,5,9,10-tetra(arylimino)pyrenylidenyldipalladium(II) tetrachloride complexes (Pd1–Pd4) was synthesized and characterized by FT-IR and NMR spectroscopy as well as elemental analysis. The molecular structures of representative complexes Pd1 and Pd2 were determined by single crystal X-ray diffraction to reveal a square planar geometry around the palladium centre. The complex Pd1 dissolved in the presence of ethanol to form mono-palladium complex C1, whose structure was also confirmed by single crystal X-ray diffraction. All binuclear palladium complexes promote the Heck cross-coupling reactions with high activities; the reaction can be carried out for various substrates and activators (basic compounds) and also in various solvents. The binuclear palladium complexes exhibit significantly higher efficiency than do their mono-palladium complexes bearing 4,5-bis(arylimino)pyrenylidenes.