Low-molecular-weight (MW) ethylene oligomers with hyperbranched microstructures are often difficult to be synthesized by traditional catalytic processes. In this study, a series of N-terphenyl iminopyridyl ligands and the corresponding Pd(II) and Ni(II) complexes bearing remote conjugated substituents with different electronic effects (H, Me, F, Cl, and tBu) were synthesized in a simple and efficient way. These Pd(II) and Ni(II) complexes were highly effective in the ethylene oligomerization and co-oligomerization with methyl acrylate (MA). Low-MW ethylene oligomers with hyperbranched microstructures were generated using the iminopyridyl Pd(II) and Ni(II) complexes in ethylene oligomerization. More importantly, polar functionalized ethylene–MA co-oligomers with low MWs and varying incorporation ratios were generated via ethylene and MA co-oligomerization using the Pd(II) complexes. Most notably, these ethylene oligomers obtained by different metal species showed a significant difference in microscopic chain architectures. The remote conjugated electron effect showed little effect on the polymerization parameters of the iminopyridyl system, which is very different from those of the salicylaldiminato system.

Recently, the second coordination sphere effect has been successfully exploited to modulate the catalytic behavior of late-transition metal catalysts in olefin insertion polymerization. In this study, four bulky iminopyridyl Ni(II) and Pd(II) complexes that contain naphthalene or benzothiophene groups were firstly prepared and their applications in olefin oligomerization were also investigated. The as-prepared nickel and palladium complexes generally displayed good catalytic activity in ethylene oligomerization, providing hyperbranched oligomers with various microstructures. Notably, the molecular weights of the ethylene oligomers generated by the benzothiophene-based Ni(II)/Pd(II) complexes were significantly lower than those generated by the naphthalene-based complexes. In addition, these palladium complexes could catalyze the co-oligomerization of ethylene and MA, yielding hyperbranched co-oligomers with tunable incorporation ratios of MA. Moreover, for ethylene oligomerization catalyzed by nickel complexes, toluene-end-functionalized branched ethylene oligomers were formed via Friedel–Crafts addition of the resulting unsaturated ethylene oligomers to the toluene solvent. In this work, we found that the second coordination sphere effect of benzothiophene could facilitate chain transfer in iminopyridyl Ni(II)/Pd(II)-catalyzed ethylene (co)oligomerization, in contrast to the phenomenon observed in the corresponding α-diimine system.

Recently, polyolefin thermoplastic elastomers can be obtained directly using ethylene as a single feedstock via α-diimine nickel-catalyzed ethylene chain walking polymerization. Here, a new range of bulky acenaphthene-based α-diimine nickel complexes with hybrid o-phenyl and -diarylmethyl anilines were constructed and applied to ethylene polymerization. All the nickel complexes under the activation of excess Et₂AlCl exhibited good activity (level of 10⁶ g mol⁻¹ h⁻¹) and produced polyethylene with high molecular weight (75.6–352.4 kg/mol) as well as proper branching densities (55–77/1000C). All the branched polyethylenes obtained exhibited high strain (704–1097%) and moderate to high stress (7–25 MPa) at break values. Most interestingly, the polyethylene produced by the methoxy-substituted nickel complex exhibited significantly lower molecular weights and branching densities, as well as significantly poorer strain recovery values (48% vs. 78–80%) than those by the other two complexes under the same conditions.

Mercury ions can be enriched along the food chain and even low concentrations of mercury ions can seriously affect human health and the environment. Therefore, rapid, sensitive, and highly selective detection of mercury ions is of great significance. In this work, we synthesized Fe₃O₄@SiO₂@Au three-layer core/shell nanoparticles, and then modified 4-MPy (4-mercaptopyridine) to form a SERS sensor. Mercury ions in water can be easily captured by 4-MPy which were used as the reporter molecules, and the concentration of mercury ions can be evaluated based on the spectral changes (intensification and reduction of peaks) from 4-MPy. After the mercury ion was combined with the pyridine ring, the peak intensity at 1093 cm⁻¹ increased with the concentration of mercury ion in the range of 10 ppm–1 ppb, while the Raman intensity ratio I (416 cm⁻¹)/I (436 cm⁻¹) decreased with the increase of mercury ion concentration. This magnetically separatable and recyclable SERS sensor demonstrates good stability, accuracy, and anti-interference ability and shows the potential to detect actual samples. Furthermore, we demonstrate that the probe is applicable for Hg²⁺ imaging in macrophage cells.