Diiminates and Diamides as Ligands in Polymerization Catalysts with M(III) (M = Ti, V, Cr) Metal Centers. A Theoretical Study
Bibliographic record
Abstract
A theoretical study has been carried out on two types of olefin polymerization catalysts based on the same M(III) centers (M = Ti, V, Cr) but different (mono) anionic ligand designs. The first system contains a mono-β-diiminato ligand that binds through the two imine nitrogens to the M(III) center and has the nitrogen lone-pairs perpendicular to the NMN coordination plane. It is shown that the generic mono-β-diiminato ligand system without bulky substituents on the nitrogen has barriers (kcal/mol) for insertion (Ti: 10.7; V: 12.2; Cr: 10.4) quite similar to the β-hydrogen transfer process (BHT) (Ti: 11.2; V: 9.8; Cr: 8.4), which serves as the chain-terminating step. The close proximity of the two barriers is in line with findings for other bidentate nitrogen ligands, where bulky aryl groups on the nitrogens were required in order to increase the BHT barrier relative to insertion and ensure acceptable molecular weights. The second system contains a bridged diamide ligand in which the ligand backbone forces the lone-pairs on the nitrogens into the NMN coordination plane and the bulk of the ligand to be below and above this plane. For this system barriers (kcal/mol) of insertion (Ti: 14.4; V: 9.7; Cr: 15.3) are calculated to be well below the barriers (Ti: 19.0; 18.7; 21.8) for the BTH process, as the BHT transition state is destabilized by the ligand backbone. Especially the V(III) system is predicted to be a good candidate as a high molecular weight polymerization catalyst.
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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) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| 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".