Revisiting the Reactivity of the Dismissed Hydrogen Atom Transfer Catalyst Succinimide-N-oxyl
Bibliographic record
Abstract
Phthalimide-N-oxyl (PINO) and related radicals are promising catalysts for C-H functionalization reactions. To date, only a small number of N-oxyl derivatives have demonstrated improved activities over PINO. We postulate that the lack of success in identifying superior catalysts is associated not only with challenges in the design and synthesis of new structures, but also the way catalysts are evaluated and utilized. Catalyst evaluation typically relies on the use of chemical oxidants to generate N-oxyl radicals from their parent N-hydroxy compounds. We put forth an example where a potential-controlled electrochemical analy-sis reveals that succinimide-N-oxyl (SINO) compares favorably to PINO as a hydrogen atom transfer catalyst – in contrast to previous claims based on other approaches. Furthermore, our efforts to understand the basis for the greater reactivity of SINO relative to PINO have shed further light on the interplay of thermodynamic and kinetic factors in these HAT reactions and sug-gest that transition state (TS) polarization is a particularly important consideration. This is illustrated by the essentially identi-cal reactivity of tetrachloro-PINO and SINO despite the significantly greater thermodynamic driving force in the reactions of the latter. Such measures of HAT TS polarization (i.e., proton affinity of the N-oxide anion) may be useful parameters in pre-dicting and/or rationalizing reactivity in addition to reaction energetics (i.e., O-H bond dissociation enthalpy of the N-OH moie-ty). Building on these insights, we report the design and initial characterization of a chlorinated SINO derivative that has signif-icantly greater reactivity as a HAT catalyst than either PINO or its chlorinated derivative.
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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 | 0.001 | 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".