Polymerization of Ethylene Catalyzed by a Nickel(+2) Anilinotropone-Based Catalyst: DFT and Stochastic Studies on the Elementary Reactions and the Mechanism of Polyethylene Branching
Bibliographic record
Abstract
The results of combined DFT/stochastic studies on the mechanism of ethylene polymerization catalyzed by a neutral Ni-anilinotropone complex are presented. The generation of active species by phosphine dissociation and chain propagation and chain isomerization reactions have been investigated. The alternative methyl acrylate binding modes have also been studied. Further, the DFT-calculated energetics of the elementary reactions have been used to model the influence of the reaction conditions ( T, P ) on the branching/microstructure of polyethylenes produced in this process. The model and real catalysts (N ∧ O−Ni; N ∧ O = −N(Ar)−(C 7 H 5 )−O−, with Ar = H and Ar = C 6 H 3 ( i -Pr) 2, respectively) have been considered to account for the electronic and steric effects. The presence of two cis / trans isomers for all the reactions has been considered. The results indicate that for the real anilinotropone catalyst the phosphine dissocciation is less endothermic (22 kcal/mol) than for the corresponding salicylaldiminato system (29 kcal/mol). The more branched alkyl agostic complexes are found to be more stable than the less branched and the linear isomers, while the stability order for the olefin-alkyl complexes is opposite. Thus, the stability of the alkyl complexes shifts the equilibrium toward formation of the branched species, while the stability of ethylene complexes favors formation of linear structures. The DFT results show that the energetically preferred pathways for the chain propagation and isomerization reactions start from the higher energy cis / trans isomers (with the alkyl positioned trans to the N atom on the catalyst). The preferred isomerization reactions have very low barriers (2.4−4.5 kcal/mol for different alkyl species). Along these pathways the unusually stable olefin-hydride complexes are formed, some of them being more stable (by 1.5−3 kcal/mol) than the alkyl agostic complexes. The results of the calculations for the methyl acrylate complexes confirm the high tolerance of the anilinotropone catalyst toward polar groups: the π-complexes are more stable by 8−13 kcal/mol than the systems with the acrylate molecule bound by its carbonyl oxygen. This functional group tolerance is larger than for the Grubbs catalyst. Also, the acrylate π-complexation energies are less affected by the steric bulk than in the case of salicylamidato catalysts and the diimine catalysts. Finally, the results of the stochastic simulations quantitatively reproduce the experimental trends in the temperature and pressure dependence of the average number of branches. In addition, the stochastic simulations provide detailed information about the variations in the topology of polyethylenes produced under different conditions.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".