Research progress of iron-based catalysts for selective oligomerization of ethylene

Adsorption and activation of small molecules on boron nitride catalysts

Hexagonal boron nitride possesses a unique layered structure, high specific surface area and similar electronic properties as graphene, which makes it not only a promising catalyst support, but also a highly effective metal-free catalyst in the booming field of green chemistry. Reactions involving small molecules (e.g., oxygen, low carbon alkanes, nitrogen and carbon dioxide) have always been a hot topic in catalytic research, especially associated with the adsorption and activation regime of different forms of small molecules on catalysts. In this review, we have investigated the adsorption of different small molecules and the relevant activation mechanisms of four typical chemical bonds (OO, C-H, NN, CO) on hexagonal boron nitride. Recent progress on approaches adopted to enhance the activation capacity such as doping, defect engineering and heterostructuring are summarized, highlighting the potential applications of nonmetallic hexagonal boron nitride catalysts in various reactions. This comprehensive investigation offers a reference point for the enhanced mechanistic understanding and future design of effective and sustainable catalytic systems based on boron nitride.

Chromium-Based Complexes Bearing Aminophosphine and Phosphine-Imine-Pyrryl Ligands for Selective Ethylene Tri/Tetramerization

A series of Cr-based complexes 6-10 bearing aminophosphine (P,N) ligands Ph₂P-L-NH₂ [L = CH₂CH₂ (1), L = CH₂CH₂CH₂ (2), and L = C₆H₄CH₂ (3)] and phosphine-imine-pyrryl (P,N,N) ligands 2-(Ph₂P-L-N=CH)C₄H₃NH [L = CH₂CH₂CH₂ (4) and L = C₆H₄CH₂ (5)] were prepared, and their catalytic properties were examined for ethylene tri/tetramerization. X-ray crystallographic analysis of complex 8 indicated the κ²-P,N bidentate coordination mode at the Cr(III) center and the distorted octahedral geometry of monomeric P,N-CrCl₃. Upon activation by methylaluminoxane (MAO), complexes 7-8 bearing P,N (PC₃N backbone) ligands 2-3 showed good catalytic reactivity for ethylene tri/tetramerization. On the other hand, complex 6 bearing the P,N (PC₂N backbone) ligand 1 was found active for non-selective ethylene oligomerization, while complexes 9-10 bearing P,N,N ligands 4-5 only produced polymerization products. In particular, the high catalytic activity of 458.2 kg/(g·Cr·h), excellent selectivity of 90.9% (1-hexene and 1-octene combined), and extremely low PE content of 0.1% were obtained with complex 7 in toluene at 45 °C and 45 bar. These results suggest that rational control of P,N and P,N,N ligand backbones, including a carbon spacer and rigidity of a carbon bridge, can lead to the high-performance catalyst for the ethylene tri/tetramerization process.