Factors Favoring Efficient Bifunctional Catalysis. Study of a Ruthenium(II) Hydrogenation Catalyst Containing an N-Heterocyclic Carbene with a Primary Amine Donor
Bibliographic record
Abstract
An alcohol-assisted outer-sphere bifunctional mechanism is proposed for the H 2 hydrogenation of ketones catalyzed by the ruthenium(II) precatalyst [RuCp*(C–NH 2 )py]PF 6 ( 2; Cp* = pentamethylcyclopentadienyl ligand, C–NH 2 = N-heterocyclic carbene (NHC) with a tethered primary amine donor, py = pyridine) when activated by an alkoxide base. It has a high activity (turnover frequency (TOF) of up to 17 600 h –1 ) and selectivity for the H 2 hydrogenation of ketones at 25 °C and 8 bar of H 2 pressure in the presence of alcohols. Computational studies of a model neutral ruthenium(II) hydride amine complex, RuCp(C–NH 2 )H (Cp = cyclopentadienyl ligand), using density functional theory (DFT) methods reveal a low free energy barrier for the transfer of a proton/hydride couple to the ketone in the outer coordination sphere. In contrast, the related iridium(III) hydride amine complex [IrCp(C–NH 2 )H] + is predicted to have a high barrier for hydride transfer to the ketone due to the poor nucleophilicity of this cationic hydride. A 2-propanol molecule acts as a proton shuttle in the heterolytic splitting of the η 2 -H 2 ligand on ruthenium according to deuterium labeling and computational studies. The carbonyl stretching wavenumbers of the complexes [RuCp*(D–NH 2 )CO]X, including the new complexes [RuCp*(C–NH 2 )CO]PF 6 ( 4 ) and [RuCp*(P–NH 2 )CO]PF 6 ( 5; P–NH 2 = 2-(diphenylphosphino)benzylamine), decrease as D is changed in the order phosphine, NHC, 2′-pyridine, amine. Thus, the NHC complex 2 is more electron rich and more active as a hydrogenation catalyst than the phosphine complex [RuCp*(P–NH 2 )py]PF 6 ( 3 ). We conclude that complex 2 outperforms other ruthenium(II) NHC complexes and some other phosphine–amine complexes for the H 2 hydrogenation of ketones due to the following factors: (1) the ease of formation of a highly reactive neutral hydride, (2) the presence of an NH 2 donor ligand required for bifunctional catalysis, and (3) the presence of an NHC donor to achieve the right balance of hydricity of the metal hydride and acidity of the protic amine group for the efficient H + /H – transfer to the polar double bond.
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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 | 0.002 |
| 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".