Abstract:The effect of ethylene tetramerisation ligand structures on 1‐octene selectivity is well studied. However, by‐product formation is less understood. In this work, a range of PNP ligand structures are correlated with the full product selectivity and with catalyst activity. As steric bulk on the N‐substituent increases, the product selectivity shifts from >10 % to < 3% of both C6 cyclics and C16+ by‐products. 1‐Octene peaks at ca. 70%. Thereafter, only 1‐hexene increases. Similar selectivity changes were observed… Show more
“…Complex 9 afforded the 58.6% selectivity toward C 8 and the 24.7% selectivity toward C 6 (45.8% 1-C 6 ). These results demonstrated that the catalytic activity and the production selectivity were mainly dependent on the electron-donating property and the steric bulk in ligands 1–3 , which was in line with the literature results. , To summarize, the experimental results also revealed that complex 7 can promote the nonselective ethylene oligomerization, while both complex 8 and complex 9 are more beneficial for the selective ethylene tri/tetramerization. Since complex 8 presented the highest C 8 selectivity and the lowest PE content, it was selected to further explore the effect of reaction conditions on the catalytic selective ethylene tri/tetramerization.…”
Section: Resultssupporting
confidence: 90%
“…The effects of reaction conditions, including the oligomerization temperature, reaction pressure, and Al/Cr molar ratio, on the catalytic selective ethylene tri/tetramerization were studied with the complex 8/MAO system to achieve the optimal catalytic response. First, the different oligomerization temperatures (40,45,50, and 55 °C) were evaluated, as shown in Figure 2a. The catalytic activity of the complex 8/ MAO system showed a volcano shape with increasing reaction temperatures from 40 to 55 °C, and the highest catalytic activity of 201.9 kg/(g Cr•h) was obtained at 45 °C.…”
Section: Effect Of Reaction Conditions On the Catalytic Behaviorsmentioning
confidence: 99%
“…17,41 Besides, the PE content (0.9%) was the lowest at 45 °C. Second, the effects of ethylene pressures (30,35,40, and 45 bar) on the catalytic activity and the product selectivity with the complex 8/MAO system at 45 °C were further studied. As shown in Figure 2b, the catalytic activity was remarkably increased from 73.1 to 207.7 kg/(g Cr•h) with the increase of ethylene pressures from 30 to 45 bar (Table 3, entries 2 and 5−7), which was mainly attributed to the improved solubility of ethylene in the toluene solvent.…”
Section: Effect Of Reaction Conditions On the Catalytic Behaviorsmentioning
A range of novel N-substituted diphosphinoamine (PNP) ligands Ph 2 PN(R)PPh 2 [R = F 2 CHCH 2 (1); R = Me 2 CHCH 2 (2); R = Me 2 CHCH 2 CH 2 (3)] have been synthesized via one-step salt elimination reaction. The ligand-coordinated chromium carbonyls [Ph 2 PN(R)PPh 2 ]Cr(CO) 4 (4−6) were further synthesized, and X-ray crystallography analysis of complex 6 revealed the κ 2 -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 {[Ph 2 PN(R)PPh 2 ]CrCl 2 (μ-Cl)} 2 (7−9) were further discussed in depth. Experimental results showed that complex 7 with the strong electron-withdrawing F 2 CHCH 2 group can promote the nonselective ethylene oligomerization, while both complex 8 and complex 9 with the electron-donating Me 2 CHCH 2 and Me 2 CHCH 2 CH 2 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.
“…Complex 9 afforded the 58.6% selectivity toward C 8 and the 24.7% selectivity toward C 6 (45.8% 1-C 6 ). These results demonstrated that the catalytic activity and the production selectivity were mainly dependent on the electron-donating property and the steric bulk in ligands 1–3 , which was in line with the literature results. , To summarize, the experimental results also revealed that complex 7 can promote the nonselective ethylene oligomerization, while both complex 8 and complex 9 are more beneficial for the selective ethylene tri/tetramerization. Since complex 8 presented the highest C 8 selectivity and the lowest PE content, it was selected to further explore the effect of reaction conditions on the catalytic selective ethylene tri/tetramerization.…”
Section: Resultssupporting
confidence: 90%
“…The effects of reaction conditions, including the oligomerization temperature, reaction pressure, and Al/Cr molar ratio, on the catalytic selective ethylene tri/tetramerization were studied with the complex 8/MAO system to achieve the optimal catalytic response. First, the different oligomerization temperatures (40,45,50, and 55 °C) were evaluated, as shown in Figure 2a. The catalytic activity of the complex 8/ MAO system showed a volcano shape with increasing reaction temperatures from 40 to 55 °C, and the highest catalytic activity of 201.9 kg/(g Cr•h) was obtained at 45 °C.…”
Section: Effect Of Reaction Conditions On the Catalytic Behaviorsmentioning
confidence: 99%
“…17,41 Besides, the PE content (0.9%) was the lowest at 45 °C. Second, the effects of ethylene pressures (30,35,40, and 45 bar) on the catalytic activity and the product selectivity with the complex 8/MAO system at 45 °C were further studied. As shown in Figure 2b, the catalytic activity was remarkably increased from 73.1 to 207.7 kg/(g Cr•h) with the increase of ethylene pressures from 30 to 45 bar (Table 3, entries 2 and 5−7), which was mainly attributed to the improved solubility of ethylene in the toluene solvent.…”
Section: Effect Of Reaction Conditions On the Catalytic Behaviorsmentioning
A range of novel N-substituted diphosphinoamine (PNP) ligands Ph 2 PN(R)PPh 2 [R = F 2 CHCH 2 (1); R = Me 2 CHCH 2 (2); R = Me 2 CHCH 2 CH 2 (3)] have been synthesized via one-step salt elimination reaction. The ligand-coordinated chromium carbonyls [Ph 2 PN(R)PPh 2 ]Cr(CO) 4 (4−6) were further synthesized, and X-ray crystallography analysis of complex 6 revealed the κ 2 -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 {[Ph 2 PN(R)PPh 2 ]CrCl 2 (μ-Cl)} 2 (7−9) were further discussed in depth. Experimental results showed that complex 7 with the strong electron-withdrawing F 2 CHCH 2 group can promote the nonselective ethylene oligomerization, while both complex 8 and complex 9 with the electron-donating Me 2 CHCH 2 and Me 2 CHCH 2 CH 2 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.
“…54 Experimentally, Makume examined purity for ethylene tetramerization with bisphosphine Cr catalysts where the steric bulk on the N-position of the ligand backbone partially controls purity. 55 As one recent example from a computational perspective, Liu and Liu used DFT calculations to understand trimerization/tetramerization selectivity for (2,2-dipicolylamine)Cr catalysts, 56,57 and in addition to the Cr charge controlling selectivity it was proposed that steric effects impact 1-hexene selectivity.…”
One approach to selectively generate 1-hexene is through ethylene trimerization using highly active Cr N-phosphinoamidine catalysts ((P,N)Cr). Depending on the ligand, (P,N)Cr catalysts can either generate nearly pure 1-hexene or form 1-hexene with significant mixtures of other C6 mass products, for example methylenecyclopentane. Here we report DFT transition state modeling examining 1-hexene catalysis pathways as well as pathways that lead to alternative C6 mass products. This provided qualitative and semi-quantitative modeling of the experimental 1-hexene purity values for several (P,N)Cr catalysts. Consistent with previous computational studies, the key 1-hexene purity-determining transition states were determined to be β-hydrogen transfer structures from the metallacycloheptane intermediate. The origin of selectivity for these (P,N)Cr catalysts can be attributed to steric effects in the transition-state structure with coordinated ethylene that leads to C6 impurities.
“…Owing to the superior material properties of the copolymers derived from 1-hexene/1-octene over other alpha olefins, the search for a catalytic system to selectively produce C 6 /C 8 a-olefins via ethylene tri-/tetramerization has witnessed a steady upsurge in recent years. [1][2][3][4][5][6][7] Most notably, following the emergence of Sasol's initial reports on tetramerization, the chromium-based pre-catalysts where the metal center is stabilized by bidentate phosphine ligands, [8][9][10][11][12][13][14][15][16][17][18] in particular bisphosphineamines (PNPs), [8][9][10][11][12] have received considerable attention. Since the N-substituents of the PNP ligands are believed to play a critical role in oligomerization performance, numerous N-functionalized PNP ligands have been developed and investigated for this purpose.…”
Novel PNP ligands bearing N-triptycene backbone was developed and evaluated for selective ethylene oligomerization. Upon activation with MMAO-3A, the pre-catalyst mixture containing Cr(acac)3/ligand efficiently promotes ethylene tetramerization with remarkably high...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.