Influence of Ring Strain and Bond Polarization on the Ring Expansion of Phosphorus Homocycles
Bibliographic record
Abstract
Heterolytic cleavage of homoatomic bonds is a challenge, as it requires separation of opposite charges. Even highly strained homoatomic rings (e.g., cyclopropane and cyclobutane) are kinetically stable and do not react with nucleophiles or electrophiles. In contrast, cycloalkanes bearing electron-donating/withdrawing substituents on adjacent carbons have polarized C–C bonds and undergo numerous heterolytic ring-opening and expansion reactions. Here we show that upon electrophile activation phosphorus homocycles exhibit analogous reactivity, which is modulated by the amount of ring strain and extent of bond polarization. Neutral rings ( t BuP) 3, 1, or ( t BuP) 4, 2, show no reactivity toward nitriles, but the cyclo-phosphinophosphonium derivative [( t BuP) 3 Me] +, [ 3Me ] +, undergoes addition to nitriles giving five-membered P 3 CN heterocycles. Because of its lower ring strain, the analogous four-membered ring, [( t BuP) 4 Me] +, [ 4Me ] +, is thermodynamically stable with respect to cycloaddition with nitriles, despite similar P–P bond polarization. We also report the first example of isonitrile insertion into cyclophosphines, which is facile for polarized derivatives [ 3Me ] + and [ 4Me ] +, but does not proceed for neutral 1 or 2, despite the calculated exothermicity of the process. Finally, we assessed the reactions of [ 4R ] + R = H, Cl, F toward 4-dimethylaminopyridine (dmap), which suggest that the site of nucleophilic attack varies with the extent of P–P bond polarization. These results deconvolute the influence of ring strain and bond polarization on the chemistry of inorganic homocycles and unlock new synthetic possibilities.
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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 | 0.000 |
| 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".