Rh-Mediated Polymerization of Carbenes: Mechanism and Stereoregulation
Bibliographic record
Abstract
Ligand variation, kinetic investigations, and computational studies have been used to elucidate the mechanism of rhodium-catalyzed diazoalkane polymerization. Variations in the "N,O" donor part of the catalyst precursors (diene)Rh(I)(N,O) result in different activities but virtually identical molecular weights, indicating that this part of the precursor is lost on forming the active species. In contrast, variation of the diene has a major effect on the nature of the polymer produced, indicating that the diene remains bound during polymerization. Kinetic studies indicate that only a small fraction of the Rh (1-5%) is involved in polymerization catalysis; the linear relation between polymer yield and M(w) suggests that the chains terminate slowly and chain transfer is not observed (near living character). Oligomers and fumarate/maleate byproducts are most likely formed from other "active" species. Calculations support a chain propagation mechanism involving diazoalkane coordination at the carbon atom, N(2) elimination to form a carbene complex, and carbene migratory insertion into the growing alkyl chain. N(2) elimination is calculated to be the rate-limiting step. On the basis of a comparison of NMR data with those of known oligomer fragments, the stereochemistry of the new polymer is tentatively assigned as syndiotactic. The observed syndiospecificity is attributed to chain-end control on the rate of N(2) elimination from diastereomeric diazoalkane complexes and/or on the migratory insertion step itself.
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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 | 0.000 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".