Part I: Backbone modification of n-heterocyclic carbenes: new ligands and applications to catalysis \n\nPart II: Large scale synthesis of NHC precursor 2,6-di(3-pentyl)aniline
Bibliographic record
Abstract
The first part of this research is focused on the development and application of backbone-modified N-heterocyclic carbene (NHC) ligands in palladium-catalyzed cross-coupling. Various backbone substituted imidazole-2-ylidine NHCs and their corresponding Pd-PEPPSI complexes were synthesized and S.A.R. studies were performed in a series of challenging cross-coupling reactions to determine the effect of backbone substitution on catalyst activity. Pd-PEPPSI-IPentCl, featuring chlorines on the backbone of our IPent NHC, was identified as one of the most active and selective catalysts yet reported in the literature in the secondary alkyl Negishi coupling, an important method for the installation of secondary alkyl groups onto aromatic systems. Mechanistic studies, supported by DFT calculations and IR spectroscopic analyses, indicate that the effect imparted by the backbone substituents is primarily steric in origin. \n\nFurther optimizing the architecture of the trans-ligated pyridine culminated in the development of Pd-PEPPSI-IPentCl-picoline, which we have shown to be a superior catalyst for the unprecedented room temperature Buchwald-Hartwig amination of aryl halides with electronically deactivated anilines using a mild carbonate base. These conditions are milder than any yet reported in the literature for the cross-coupling of anilines and represent a significant advance in the field. \n\nThe second part of this research deals with the development of a method for the large-scale preparation of 2,6-di(3-pentyl)aniline, a precursor to the IPent family of novel, highly active NHC ligands. Our newly developed synthetic route features a Pd-catalyzed cross-coupling of 3-lithio-2-pentene, derived from 3-pentanone, to readily available 2,6-dibromoaniline. This new sequence represents a significant improvement in overall process efficiency in the form of a lower step count, higher product yield, and increased reproducibility relative to earlier syntheses. Since its inception, this method has been applied successfully towards the synthesis of nearly 0. 7 kg of 2,6-di(3-pentyl)aniline and has the potential for larger scale implementation.
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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 | 0.001 |
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".