Optimization of Synthetically Versatile Pyridylidene Amide Ligands for Efficient Iridium‐Catalyzed Water Oxidation
Bibliographic record
Abstract
Abstract The synthetic versatility of pyridylidene amide (PYA) ligands has been exploited to prepare and evaluate a diverging series of iridium complexes containing C,N‐bidentate chelating aryl‐PYA ligands for water oxidation catalysis. The phenyl‐PYA lead structure 1 was modified (i) electronically through introduction of one, two, or three electron‐donating methoxy substituents on the aryl ring, (ii) by incorporating long aliphatic chains to the pyridyl fragment of the PYA unit, and (iii) by altering the PYA positions from para‐PYA to its ortho‐ and meta‐isomers. Electrochemistry indicated no substantial electronic effect of the aliphatic chains, and only minor changes of the electron density at iridium when modifying the aryl ligand site, yet substantial alteration if the PYA ligand is the ortho‐ (E1/2=+0.72 V), para‐ (E1/2=+0.64 V), or meta‐isomer (E1/2=+0.56 V vs. saturated calomel electrode; SCE). In water oxidation catalysis, the long alkyl chains did not induce any rate enhancement compared with the phenyl‐PYA lead compound, whereas MeO groups incorporated in the aryl group enhanced the catalytic activity from a turnover frequency (TOFmax)=1600 h−1 in the original Ph‐PYA system gradually as more MeO groups were introduced up to a TOFmax=3300 h−1 for a tris(MeO)‐substituted aryl‐PYA system. The variation of the PYA substitution had only a minor impact on catalytic activity and revealed only a weak trend in the sequence ortho>meta>para. The high activity of the tris(MeO) system and the ortho‐PYA isomer were attributed to efficient hydrogen bonding, which assists O−H bond activation and proton transfer. Remarkably, merging of the two optimized motifs, that is, an aryl unit with three MeO substituents and the PYA as the ortho isomer, into a single new aryl‐PYA ligand system failed to improve the catalytic activity. Computational analysis suggests too much congestion at the active site, which hinders catalytic turnover. These results illustrate the complexity of ligand design and the subtle effects at play in water oxidation catalysis.
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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".