Ethylene tri-/tetramerization catalysts supported by diphosphinothiophene ligands

Highly active chromium-based selective ethylene tri-/tetramerization catalysts supported by alkenylphosphanyl PNP ligands

A series of novel diphosphinoamine (PNP) ligands bearing a P-alkenyl group were synthesized and applied in chromium-catalyzed selective ethylene tri-/tetramerization by in situ combination of Cr(acac)3 and modified methylalumoxane (MMAO-3A). The ligand substitution and oligomerization conditions have a remarkable influence on the catalytic activity and controllable selectivity. Most of these PNP ligands are highly active for ethylene tri-/tetramerization with considerable selectivity. An asymmetric diisopropenylphosphanyl ligand with an N-cyclohexyl group achieved the highest activity of 2036 kg (g Cr h-1)-1 with a high total selectivity of 81.1 wt% toward valuable 1-hexene (43.0 wt%) and 1-octene (38.1 wt%) at 40 bar ethylene and 60 °C. An asymmetric mixed isopropenyl/ethylphosphanyl ligand with an N-isopropyl group exhibited a high 1-octene selectivity of 65.5 wt% and a high total 1-hexene/1-octene selectivity (91.5 wt%) with a high activity of 1256 kg (g Cr h-1)-1.

Chromium Catalysts for Selective Ethylene Oligomerization Featuring Binuclear PNP Ligands

A series of novel binuclear PNP ligands based on the cyclohexyldiamine scaffold were synthesized for this study. The experimental results showed that positioning the two PNP sites at the para-positions of the cyclohexyl framework led to a significant enhancement in the catalytic activity for selective tri/tetramerization of ethylene. The PNP/Cr(acac)3/MAO(methylaluminoxane) catalytic system exhibited relatively high catalytic activity (up to 3887.7 kg·g-1·h-1) in selective ethylene oligomerization with a total selectivity of 84.5% for 1-hexene and 1-octene at 40 °C and 50 bar. The relationship between the ligand structure and ethylene oligomerization performance was further explored using density functional theory calculations.

Chromium-Based Complexes Bearing N-Substituted Diphosphinoamine Ligands for Ethylene Oligomerization

A range of novel N-substituted diphosphinoamine (PNP) ligands Ph₂PN(R)PPh₂ [R = F₂CHCH₂ (1); R = Me₂CHCH₂ (2); R = Me₂CHCH₂CH₂ (3)] have been synthesized via one-step salt elimination reaction. The ligand-coordinated chromium carbonyls [Ph₂PN(R)PPh₂]Cr(CO)₄ (4-6) were further synthesized, and X-ray crystallography analysis of complex 6 revealed the κ²-P,P bidentate binding mode of Cr center and the molecular structure of PNP ligand 3. Then the catalytic ethylene oligomerization behaviors of PNP ligands 1-3 bridging chromium chloride complexes {[Ph₂PN(R)PPh₂]CrCl₂(μ-Cl)}₂ (7-9) were further discussed in depth. Experimental results showed that complex 7 with the strong electron-withdrawing F₂CHCH₂ group can promote the nonselective ethylene oligomerization, while both complex 8 and complex 9 with the electron-donating Me₂CHCH₂ and Me₂CHCH₂CH₂ groups can significantly enhance the selective ethylene tri/tetramerization. The good catalytic activity of 198.3 kg/(g Cr·h), the selectivity toward 1-hexene and 1-octene of 76.4%, and the low PE content of 0.2% were simultaneously achieved with the Al/Cr molar ratio of 600 using the complex 8/MMAO system at 45 °C and 45 bar. These excellent results were mainly attributed to the fact that the β-branching of bridging ligand 2 increased the steric bulk of the N-moiety for complex 8.

Ethylene oligomerisation chromium catalysts with unsymmetrical PCNP ligands

Chromium(iii) complexes of chelating diphosphines, with PNP or PCNCP backbones, are excellent catalysts for ethylene tetra- and/or trimerisations. A missing link within this ligand series are unsymmetric chelating diphosphines based on a PCNP scaffold. New bidentate PCNP ligands of the type Ph₂PCH₂N(R)PPh₂ (R = 1-naphthyl or 5-quinoline groups, 2a-d) have been synthesised and shown to be extremely effective ligands for ethylene tri-/tetramerisations. Three representative tetracarbonyl Cr⁰ complexes bearing a single PN(R)P (5), PCN(R)P (6), or PCN(R)CP (7) diphosphine (R = 1-naphthyl) have been prepared from Cr(CO)₄(η⁴-nbd) (nbd = norbornadiene). Furthermore we report a single crystal X-ray diffraction study of these compounds and discuss their structural parameters.

Effect of an additional donor on decene formation in ethylene oligomerization catalyzed by a Cr/PCCP system: a combined experimental and DFT study

Cr catalyst based on a PCCP ligand shows high activity in ethylene oligomerization, giving 1-hexene and considerable C₁₀ fraction. DFT calculation results are consistent with the experimental observations on the distribution of C₁₀ isomers.

Chromium complexes supported by the bidentate PN ligands: synthesis, characterization and application for ethylene polymerization

Chromium-based complexes are among the most important catalysts in the field of ethylene polymerization and oligomerization. Heterogeneous Cr Phillips catalysts account for more than one-third of the commercialized high density polyethylene (HDPE). In this contribution, chromium complexes, LCrCl3 (Cr1-Cr4: L = 2,6-R1-4-R2-C6H2-N[double bond, length as m-dash]CH-C6H4-2-PPh2; Cr1: R1 = H, R2 = H; Cr2: R1 = Me, R2 = H; Cr3: R1 = iPr, R2 = H; Cr4: R1 = Ph2CH, R2 = iPr), have been synthesized and characterized by elemental analysis, ESI and IR spectroscopy. The molecular structures of Cr3 and Cr4 are defined by X-ray diffraction, revealing a distorted octahedral geometry around the chromium center in both structures. In the presence of an aluminum cocatalyst, complexes Cr1-Cr4 show moderate to high activities toward ethylene polymerization. The nature of the catalysts and various reaction conditions, such as the nature and the amount of cocatalyst, reaction time and temperature, are investigated in detail. The results show that the title complexes have good thermal stability and the substituents on the ligands significantly affect the catalytic properties. Particularly, complex Cr4 can produce HDPE with a high molecular weight up to 68.3 × 104 g mol-1 due to the suppression of the chain transfer/termination by the introduction of bulky Ph2CH groups.

Regiospecific and stereoselective synthesis of (E)- and (Z)-2-phosphino-1-alkenyl boronates via Cu-catalyzed hydroboration of alkynylphosphines

The regiospecific and stereoselective synthesis of (E)- and (Z)-2-phosphino-1-alkenyl boronates via Cu-catalyzed hydroboration of alkynylphosphines has been developed.