[2+2] versus [3+2] Addition of Metal Oxides Across CC Double Bonds: Toward an Understanding of the Surprising Chemo- and Periselectivity of Transition-Metal-Oxide Additions to Ketene
Bibliographic record
Abstract
The peri-, chemo-, stereo-, and regioselectivity of the addition of the transition-metal oxides OsO4 and LReO3 (L = O-, H3PN, Me, Cp) to ketene were systematically investigated using density-functional methods. While metal-oxide additions to ethylene have recently been reported to follow a [3+2] mechanism only, the calculations reveal a strong influence of the metal on the periselectivity of the ketene addition: OsO4 again prefers a [3+2] pathway across the C=C moiety whereas, for the rhenium oxides LReO3, the [2+2] barriers are lowest. Furthermore, a divergent chemoselectivity arising from the ligand L was found: ReO4- and (H3PN)ReO3 add across the C=O bond while MeReO3 and CpReO3 favor the addition across the C=C moiety. The calculated energy profile for the MeReO3 additions differs from the CpReO3 energy profile by up to 45 kcal/mol due to the stereoelectronic flexibility of the Cp ligand adopting eta5, eta3, and eta1 bonding modes. The selectivity of the cycloadditions was rationalized by the analysis of donor-acceptor interactions in the transition states. In contrast, metal-oxide additions to diphenylketene probably follow a different mechanism: We give theoretical evidence for a zwitterionic intermediate that is formed by nucleophilic attack at the carbonyl moiety and undergoes a subsequent cyclization yielding the thermodynamically favored product. This two-step pathway is in agreement with the results of recent experimental work.
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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 | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| 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".