Accessing Functionalized Ultra-High Molecular Weight Poly(α-olefin)s via Hafnium-Mediated Highly Isospecific Copolymerization.

Inspired by the favorable impact of heteroatom-containing groups in phenoxy-imine titanium and late transition metal catalysts, a series of novel pyridylamido hafnium catalysts bearing ─OMe (Cat-OMe), ─CF3 (Cat-CF3), and ─C6F5 (Cat-C6F5) substituents are designed and synthesized. Together with the established hafnium catalysts Cat-H and Cat-iPr by Dow/Symyx, these catalysts are applied in the polymerization of α-olefins, including 1-hexene, 1-octene, and 4M1P, as well as in the copolymerization of these α-olefins with a specifically designed polar monomer. The enhancement of polymer molecular weight derived from catalyst modification and the incorporation of polar monomers is discussed in detail. Notably, the new catalysts are all highly active for α-olefins polymerization, with catalyst Cat-CF3 producing isotactic polymers with the highest molecular weight (Mw = 1649 kg mol-1); in copolymerization with polar monomers, catalyst Cat-OMe yields isotactic copolymer with the highest molecular weight (Mw = 2990 kg mol-1). Interestingly, catalyst Cat-C6F5 bearing a ─C6F5 group in the N-aryl moiety gives rise to poly(α-olefin) with reduced stereoselectivity. The findings of this study underscore the potential of heteroatom-containing groups in the development of early transition metal catalysts and the synthesis of polymer with novel structures.

Aqueous Coordination-Insertion Copolymerization for Producing High Molecular Weight Polar Polyolefins.

Hydrocarbons, when used as the medium for transition metal catalyzed organic reactions and olefin (co-)polymerization, are ubiquitous. Environmentally friendly water is highly attractive and long-sought, but is greatly challenging as coordination-insertion copolymerization reaction medium of olefin and polar monomers. Unfavorable interactions from both water and polar monomer usually lead to either catalyst deactivation or the formation of low-molecular-weight polymers. Herein, we develop well-behaved neutral phosphinophenolato nickel catalysts, which enable aqueous copolymerization of ethylene and diverse polar monomers to produce significantly high-molecular-weight linear polar polyolefins (219-549 kDa, 0.13-1.29 mol %) in a single-component fashion under mild conditions for the first time. These copolymerization reactions occur better in water than in hydrocarbons such as toluene. The dual characteristics of high molecular weight and the incorporation of a small amount of functional group result in improved surface properties while retain the desirable intrinsic properties of high-density polyethylene (HDPE).

Efficient Suppression of Chain Transfer and Branching via Cs -Type Shielding in a Neutral Nickel(II) Catalyst.

An effective shielding of both apical positions of a neutral NiII active site is achieved by dibenzosuberyl groups, both attached via the same donors' N-aryl group in a Cs -type arrangement. The key aniline building block is accessible in a single step from commercially available dibenzosuberol. This shielding approach suppresses chain transfer and branch formation to such an extent that ultrahigh molecular weight polyethylenes (5×106  g mol-1 ) are accessible, with a strictly linear microstructure (<0.1 branches/1000C). Key features of this highly active (4.3×105  turnovers h-1 ) catalyst are an exceptionally facile preparation, thermal robustness (up to 90 °C polymerization temperature), ability for living polymerization and compatibility with THF as a polar reaction medium.

Mammalian Target of Rapamycin Complex 1 Signaling Is Required for the Dedifferentiation From Biliary Cell to Bipotential Progenitor Cell in Zebrafish Liver Regeneration.

The liver has a high regenerative capacity. Upon two-thirds partial hepatectomy, the hepatocytes proliferate and contribute to liver regeneration. After severe liver injury, when the proliferation of residual hepatocytes is blocked, the biliary epithelial cells (BECs) lose their morphology and express hepatoblast and endoderm markers, dedifferentiate into bipotential progenitor cells (BP-PCs), then proliferate and redifferentiate into mature hepatocytes. Little is known about the mechanisms involved in the formation of BP-PCs after extreme liver injury. Using a zebrafish liver extreme injury model, we found that mammalian target of rapamycin complex 1 (mTORC1) signaling regulated dedifferentiation of BECs and proliferation of BP-PCs. mTORC1 signaling was up-regulated in BECs during extreme hepatocyte ablation and continuously expressed in later liver regeneration. Inhibition of mTORC1 by early chemical treatment before hepatocyte ablation blocked the dedifferentiation from BECs into BP-PCs. Late mTORC1 inhibition after liver injury reduced the proliferation of BP-PC-derived hepatocytes and BECs but did not affect BP-PC redifferentiation. mTOR and raptor mutants exhibited defects in BEC transdifferentiation including dedifferentiation, BP-PC proliferation, and redifferentiation, similar to the chemical inhibition. Conclusion: mTORC1 signaling governs BEC-driven liver regeneration by regulating the dedifferentiation of BECs and the proliferation of BP-PC-derived hepatocytes and BECs.

Phase interface engineering of metal selenides heterostructure for enhanced lithium-ion storage and electrocatalysis.

Biphasic or multiphase heterostructures hold attractive prospects in engineering advanced electrode materials for energy-related applications owing to the appealing synergistic effect; however, they still suffer from unsatisfied electrochemical activity and reaction kinetics. Herein, guided by density functional theory calculation, a well-engineered selenides heterostructure with high-density Ni3Se4-NiSe2 biphasic interfaces that fastened in N, O-codoped carbon matrix, was developed for high-performance lithium storage and electrocatalysis. By controlled selenylation of metal-organic framework (MOF), a series of NiSex@C hybrids (Ni3Se4@C, Ni3Se4/NiSe2@C-1, Ni3Se4/NiSe2@C-2, and NiSe2@C) with tunable biphasic components and grain sizes were prepared. Abundant two-phase interfaces with higher interface density are generated inside the Ni3Se4/NiSe2-1 induced by much smaller nanograins in comparison with the Ni3Se4/NiSe2-2, so that significant charge redistribution and faster electrons/Li+ ions transfer kinetics are achieved within the selenides, which are proved by the mutual verification of experiment and theoretical analysis. Benefitting from this optimized heterointerfaces, the Ni3Se4/NiSe2@C-1 electrode manifests reduced polarization, superior rate capability, and prolonged cyclic stability (621.3 mAh g-1 at 1 A g-1 for 1000 cycles; 362.3 mAh g-1 at 4 A g-1 for 2000 cycles) with respect to the Ni3Se4/NiSe2@C-2, as well as excellent performance in LiCoO2//Ni3Se4/NiSe2@C-1 full cell. Detailed electrochemical analysis confirmed rapid electrons/Li+ diffusion rates and more pseudocapacitive energy for the Ni3Se4/NiSe2@C-1. Therefore, the Ni3Se4/NiSe2@C-1 showcases superior hydrogen evolution reaction (HER) and lithium storage performance. This work demonstrates the significance of interface modulation to boost the electrochemical performance of multiphase heterostructures for energy storage and conversion.

Systematic studies on dibenzhydryl and pentiptycenyl substituted pyridine-imine nickel(ii) mediated ethylene polymerization.

As the analogues of classical α-diimine nickel catalysts, pyridine-imine nickel catalysts are of great interest for olefin polymerization to produce low molecular weight and branched polyethylenes. In this contribution, pyridine-imine nickel complexes Ni1-Ni4 bearing dibenzhydryl- and pentiptycenyl-N-aryl substituents and H- and Me-imine backbones were synthesized and systematically studied for ethylene polymerization. X-ray diffraction studies revealed that Ni1, Ni2 and Ni4 adopted a monoligated/binuclear structure, while Ni3 was found to adopt a monoligated/mononuclear structure, which differed from the bisligated/mononuclear mode reported previously. Upon activation with aluminum reagents such as Et2AlCl, MAO or MMAO, all these nickel complexes displayed very high activities (up to 14 530 kg mol-1 h-1) for ethylene polymerization. Branched (12-69/1000C) polyethylenes with low molecular weights (Mw: 0.7-22.1 kDa) were obtained with internal double bonds as the predominant unsaturated groups. The influences of the catalyst structure, type and amount of cocatalyst, time, temperature, pressure, and polar additive on the catalytic performances were thoroughly investigated.

Well-defined phosphino-phenolate neutral nickel(II) catalysts for efficient (co)polymerization of norbornene and ethylene.

Phosphino-phenolate neutral nickel catalysts 1-3/B(C6F5)3, without the help of any organoaluminum compound, were found to be efficient catalytic systems for norbornene polymerization and its copolymerization with norbornene derivatives. The amount of B(C6F5)3 required for achieving a high efficiency (3 equiv.) was markedly lower compared to previous reports, and high molecular weight polymers were obtained (>10(6) g mol(-1)). Efficient incorporation of polar monomers NBC, NBA, and NBM was also achieved in a controllable fashion, yielding high molecular weight copolymers. Catalysts 1-3 were highly active for ethylene polymerization as single component catalysts, with an activity of up to 10(7) g molNi(-1) h(-1), and catalyst 3 was more readily initiated at lower temperature. Catalysts 1-3 were also efficient in incorporating norbornene (up to 30%) into the polyethylene backbone. Bisligated phosphino-phenolate nickel complex 4 and salicylaldimine complex 5 were also studied for comparison, which further verified the unique performance of catalysts 1-3. Preliminary NMR analyses were conducted to explore the norbornene polymerization mechanism.

Synthesis and characterization of the titanium complexes bearing two regioisomeric trifluoromethyl-containing enaminoketonato ligands and their behavior in ethylene polymerization.

A series of new titanium complexes bearing two regioisomeric trifluoromethyl-containing enaminoketonato ligands (3a-h and 6a-h), [PhN=CRCHC(CF3)O]2TiCl2 (3a, R = Me; 3b, R = n-C5H11; 3c, R = i-Pr; 3d, R = Cy; 3e, R = t-Bu; 3f, R = CH=CHPh; 3g, R = Et; 3h, R = n-C11H23) and [PhN=C(CF3)CHC(R)O]2TiCl2 (6a, R = Ph; 6b, R = n-C5H11; 6c, R = i-Pr; 6d, R = Cy; 6e, R = t-Bu; 6f, R = CH=CHPh; 6g, R = CHPh2; 6h, R = CF3) have been synthesized and characterized. X-ray crystal structures analyses suggest that complexes 3c-e and 6c-d all adopt a distorted octahedral geometry around the titanium center. Complexes 3c, 3d and 6c display a cis-configuration of the two chlorine atoms around the titanium center, while complex 6d shows a trans-configuration of the two chlorine atoms. Especially, the configurational isomers (cis and trans) of complex 3e were identified both in solution and in the solid state by NMR and X-ray analyses. With modified methylaluminoxane as a cocatalyst, all the complexes are active towards ethylene polymerization, and produce high molecular weight polymers. With the variation of the relative position of the imino group and the trifluoromethyl group of the beta-enaminoketonato ligands, the polymerization behavior of the catalysts changed remarkably. It is observed that the substituent directly joined to the carbonyl in the ligands plays an important role for both the catalytic activities and the properties of the polymers produced.