An Addition–Isomerization Mechanism for the Anionic Polymerization of MesP═CPh<sub>2</sub> and <i>m</i>-XylP═CPh<sub>2</sub>
Bibliographic record
Abstract
We report that the anionic polymerization of P-mesityl and m -xylyl-substituted phosphaalkenes follows an unusual addition–isomerization mechanism. Specifically, the polymerization of ArP═CPh 2 [Ar = Mes ( 1a ), m -Xyl ( 1b )] involves the hindered nucleophilic anion intermediate, Ⓟ–P(Ar)–CPh 2 –, which undergoes a proton migration from the o -CH 3 of the Mes/ m -Xyl moiety to the −CPh 2 moiety to afford a propagating benzylic anion. This mechanism is supported by the preparation of model compounds MeP(CHPh 2 )-4,6-Me 2 C 6 H 2 –2-CH 2 –CPh 3 ( 2a ) or MeP(CHPh 2 )-6-MeC 6 H 3 –2-CH 2 –CPh 3 ( 2b ), which were both crystallographically characterized. Polymerization of 1a or 1b in THF solution using n -BuLi (2 mol %) revealed 1 H and 13 C NMR signals assigned to −CH 2 – and −CHPh 2 groups consistent with an addition–isomerization polymerization mechanism to afford poly(methylenephosphine) 3a or 3b . A large kinetic isotope effect (≤23) was determined for the n -BuLi-initiated polymerization of 1a - d 9 compared to 1a in THF at 50 °C, consistent with C–H (or C–D) activation as the rate-determining step. This C–H activation step was modeled using DFT computations which revealed that the intramolecular proton transfer from the o -CH 3 of the Mes moiety to the −CPh 2 moiety has an activation energy ( E a = +18.5 kcal mol –1 ). For comparison, this computational value was quite close to the experimentally measured activation energy of propagation ArP═CPh 2 in THF [ E a = 14.0 ± 0.9 kcal mol –1 ( 1a ), 15.6 ± 2.8 kcal mol –1 ( 1b )].
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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 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| 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".