Combined Density Functional Theory and Molecular Mechanics (QM/MM) Study of Single-Site Ethylene Polymerization and Chain Termination for the Catalysts [(C<sub>6</sub>R<sub>5</sub>NCH)C<sub>4</sub>H<sub>3</sub>N]<sub>2</sub>PrTi<sup>+</sup> (R = F, H) and [bis(η<sup>5</sup>-1-indenyl)dimethylsilane]PrZr<sup>+</sup> in the Presence of the Counterion CH<sub>3</sub>B(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub><sup>-</sup>
Bibliographic record
Abstract
Calculations, using density functional theory, have been carried out to investigate two chain termination processes, (i) unimolecular hydrogen transfer to the metal center and (ii) bimolecular hydrogen transfer to the incoming ethylene monomer, for the PI systems [(C 6 R 5 N CH)C 4 H 3 N] 2 PrTi-μ-CH 3 -B(C 6 F 5 ) 3 (R = F, H). A validated QM/MM model was used to represent the counterion. The barriers for the unimolecular termination process were about 36.5 kcal/mol for both the PI systems studied, while the rate-determining uptake barriers for the bimolecular chain termination process were about 18 kcal/mol lower for both PI systems. A difference of only about 0.5 kcal/mol was observed between the corresponding barriers for each of the termination processes for the two systems. The insertion of the ethylene monomer into the Ti−C bond was also investigated for the two PI systems, and the rate-determining uptake barrier was found to be about 6 kcal/mol lower than the corresponding rate-determining uptake barriers for bimolecular termination. The effect of increasing the steric bulk on the phenyl groups attached to the imine nitrogen was investigated for the [(C 6 R 5 N CH)C 4 H 3 N] 2 PrTi-μ-CH 3 -B(C 6 F 5 ) 3, with the hydrogen at the ortho position of the phenyl rings being replaced by tertiary butyl groups, modeled by MM atoms. The rate-determining uptake barrier for the bimolecular chain termination process for this system was found to be only marginally higher than the corresponding uptake barrier for the non-bulky system. Insertion and uni- and bimolecular termination processes were also investigated for the ansa -indenyl system [bis(η 5 -1-indenyl)dimethylsilane]ZrPr-μ-Me-B(C 6 F 5 ) 3 . The barriers for insertion and bimolecular chain termination for this system were comparable to those for the PI systems, but the barrier to unimolecular chain termination was found to be about 5 kcal/mol higher.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.011 | 0.005 |
| Meta-epidemiology (narrow) | 0.007 | 0.007 |
| Meta-epidemiology (broad) | 0.007 | 0.003 |
| Bibliometrics | 0.004 | 0.009 |
| Science and technology studies | 0.004 | 0.004 |
| Scholarly communication | 0.002 | 0.004 |
| Open science | 0.005 | 0.004 |
| Research integrity | 0.004 | 0.005 |
| Insufficient payload (model declined to judge) | 0.000 | 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; both teacher heads agree on what is shown here.
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".