Enantioselective Hydrogenation Catalysis Aided by a σ-Bonded Calix[4]arene to a<i>P</i>-Chirogenic Aminophosphane Phosphinite Rhodium Complex
Bibliographic record
Abstract
The first P -chirogenic aminophosphane−phosphinite (AMP*P) ligand ( 4a ) supported on the upper rim of a calix[4]arene moiety was synthesized in two steps using the ephedrine methodology. Ligand 4a was used for the preparation of the corresponding rhodium complex [Rh(COD)(AMP*P)]BF 4 ( 5a ) (COD = 1,8-cyclooctadienyl), which was tested for asymmetric catalyzed hydrogenation of various substrates. The structures of the AMP*P ligand as diborane and rhodium complexes 3a and 5a were established by X-ray analysis. The asymmetric hydrogenation catalyzed with the Rh complex 5a exhibits excellent enantioselectivities up to 98%. Investigation of modified P -chirogenic aminophosphane−phosphinite ligands 4b, c, bearing an isoelectronic or a sterically similar substituent on the P -chirogenic aminophosphane unit, demonstrates that the calix[4]arene substituent of the aminophosphane moiety plays a major role in the better asymmetric induction. The enantioselectivity of the catalyzed hydrogenation was weakly influenced by the hydrogen pressure, which is in good agreement with a stereodetermining step involving the substrate−rhodium complexes. Computer modeling indicated the presence of two conformers for the active AMP*P rhodium species, according to whether the rhodium metal is outside or inside the calix[4]arene cavity (called outer and inner ). It is obvious that the complexation of the substrate with the active rhodium species forces this complex to adopt fully the outer conformation and hence explains why the calixarene fragment plays a key role in the stereodetermining step.
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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) | 0.001 | 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".