Iridium and Rhodium Complexes Containing Enantiopure Primary Amine-Tethered <i>N</i>-Heterocyclic Carbenes: Synthesis, Characterization, Reactivity, and Catalytic Asymmetric Hydrogenation of Ketones
Bibliographic record
Abstract
The imidazolium salt [( S, S )- t BuNC 3 H 3 NCHPhCHPhNH 2 ]PF 6, ( S, S )-11· HPF 6 is a precursor to the enantiopure “Kaibene” ligand, t Bu-Kaibene, ( S, S )-11 featuring a tert -butyl group on the N -heterocyclic carbene (NHC) ring-nitrogen atoms. It has been prepared in high yield and purity by refluxing a chiral cyclic sulfamidate with 1- tert -butylimidazole. Similarly ( S, S )-12· HPF 6 with a mesityl group at the imidazolium ring-nitrogen atom has been prepared in the same fashion and serves as a source of Mes-Kaibene, ( S, S )-12 . These bidentate Kaibene ligands feature an NHC and a primary amine separated by a chiral linker. Salts ( S, S )-11· HPF 6 or ( S, S )-12· HPF 6 react with base and AgI or CuI to give a total of four M(Kaibene) 2 I compounds (M = Ag or Cu). At 22 °C, the amine-functionalized imidazolium cations undergo oxidative addition to iridium(I) in [IrCl(cod)] 2 (cod = 1,5-cyclooctadiene) to generate iridium(III) hydride R-Kaibene compounds [IrHCl(cod)( ( S, S )-11 )](PF 6 ) ( 17 ) and [IrHCl(cod)( ( S, S )-12 )](PF 6 ) ( 18 ), respectively, each as a mixture of six configurational isomers. In contrast, the salt ( S, S )-11· HPF 6 reacts with [Ir(O t Bu)(cod)] 2 to produce a bimetallic iridium compound with ( S, S )-11 as the bridging ligand. This compound contains interesting NH···Cl and NH···Ir noncovalent intramolecular interactions. Salt ( S, S )-12· HPF 6 reacts with silver oxide to yield [Ag 2 ( ( S, S )-12 ) 2 ](PF 6 ) 2 ( 20 ). Reagent 20 serves as an efficient transmetalation reagent to deliver to each rhodium in [RhCl(cod)] 2 1 equiv of ( S, S )-12 as a bidentate ligand to give [Rh(cod)( ( S, S )-12 )](PF 6 ). In the reaction between [IrCl(cod)] 2 and 20, ( S, S )-12 ends up coordinated in an iridium(III) hydride complex ( 22 ) as a tridentate ligand via the NHC, NH 2, and a cyclometalated phenyl group. The two iridium hydride compounds, 18 and 22, are catalysts for the hydrogenation of a range of ketones (turnover number up to 499, turnover frequency up to 249 h –1, with er (enantiomeric ratio) up to 35:65 R: S ).
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| 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) | 0.000 | 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 teacher head, 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".