Reactivity of Cr(III) μ-Oxo Compounds: Catalyst Regeneration and Atom Transfer Processes
Bibliographic record
Abstract
Oxidation of CpCr[(XylNCMe)(2)CH] (Xyl = 2,6-Me(2)C(6)H(3)) with pyridine N-oxide or air generated the μ-oxo dimer, {CpCr[(XylNCMe)(2)CH]}(2)(μ-O). The μ-oxo dimer was converted to paramagnetic Cr(III) CpCr[(XylNCMe)(2)CH](X) complexes (X = OH, O(2)CPh, Cl, OTs) via protonolysis reactions. The related Cr(III) alkoxide complexes (X = OCMe(3), OCMe(2)Ph) were prepared by salt metathesis and characterized by single crystal X-ray diffraction. The interconversion of the Cr(III) complexes and their reduction back to Cr(II) with Mn powder were monitored using UV-vis spectroscopy. The related CpCr[(DepNCMe)(2)CH] (Dep = 2,6-Et(2)C(6)H(3)) Cr(II) complex was studied for catalytic oxygen atom transfer reactions with PPh(3) using O(2) or air. Both Cr(II) complexes reacted with pyridine N-oxide and γ-terpinene to give the corresponding Cr(III) hydroxide complexes. When CpCr[(DepNCMe)(2)CH] was treated with pyridine N-oxide in benzene in the absence of hydrogen atom donors, a dimeric Cr(III) hydroxide product was isolated and structurally characterized, apparently resulting from intramolecular hydrogen atom abstraction of a secondary benzylic ligand C-H bond followed by intermolecular C-C bond formation. The use of very bulky hexaisopropylterphenyl ligand substituents did not preclude the formation of the analogous μ-oxo dimer, which was characterized by X-ray diffraction. Attempts to develop a chromium-catalyzed intermolecular hydrogen atom transfer process based on these reactions were unsuccessful. The protonolysis and reduction reactions of the μ-oxo dimer were used to improve the previously reported Cr-catalyzed radical cyclization of a bromoacetal.
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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 | 0.001 | 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".