Density Functional Theory Investigation into the Stereocontrol of the Syndiospecific Polymerization of Propylene Catalyzed by<i>C</i><i><sub>s</sub></i>-Symmetric Zirconocenes
Bibliographic record
Abstract
The mechanisms of the two most likely routes for the generation of stereodefects in the syndiospecific polymerization of propylene, mediated by the C s -symmetric ansa -zirconocenes Me 2 CCpFluZrR + X - ( 1 ), Me 2 CCp(3,6-di-Me-Flu)ZrR + X - ( 2a ), Me 2 SiCp(3,6-di-Me-Flu)ZrR + X - ( 2b ), and Me 2 CCp(3,6-di-tBu-Flu)ZrR + X - ( 3 ) (X - = MeB(C 6 F 5 ) 3 -, FAl(Bip f ) 3 -, MAOMe - ) are explored using density functional theory. Site epimerization events (also known as back-skip or missed insertion) generate defective single m dyads, while enantiomeric misinsertions are the main source of double mm triads. The most important factor affecting the frequency of enantiomeric misinsertion is the structure of the ligand, while the counterion and solvation have little effect. Site epimerization is also influenced by the nature of the ligand system, but the bulk and the charge distribution of the anion are more prominent factors. The inclusion of solvent effects in the modeling of the site epimerization is critical for explaining reactivity and to achieving at least qualitatively correct results. Application of the two-parameter probabilistic scheme developed by Farina and co-workers allows for the prediction of pentad distributions from the computed selectivities. The good agreement found between experiment and computations for the basic unsubstituted system invented by Ewen and Razavi validates the proposed model. Thus, the computed pentad distributions may be used for assessing the effectiveness of modifications to the ligands on syndioselectivity. Increasing the bulk of 3,6-substituents on the fluorenyl ligand leads to increased syndiotacticity, without significantly affecting the reactivity. By introducing a stereogenic center on the alkyl chain, it is possible to assess the influence of chain end control on stereoselectivity. The main effect of chain end control is to increase the stereoselectivity after a stereoerror.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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 | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.002 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.002 | 0.001 |
| Research integrity | 0.002 | 0.002 |
| Insufficient payload (model declined to judge) | 0.004 | 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".