C−H Activation of Substituted Arenes by Tungsten Alkylidene Complexes: Products, Selectivity, and Mechanism
Bibliographic record
Abstract
Thermolyses (70 °C, 40 h) of Cp*W(NO)(CH 2 CMe 3 ) 2 ( 1 ) and Cp*W(NO)(CH 2 CMe 3 )(CH 2 C 6 H 5 ) ( 2 ) in xylenes, mesitylene, and α,α,α-trifluorotoluene generate mixtures of the corresponding aryl and/or benzyl products derived from aromatic sp 2 and benzylic sp 3 C−H bond activations of the solvent molecules by the intermediate alkylidene complexes Cp*W(NO)( CHCMe 3 )(σ-CMe 4 ) (σ- A ) and Cp*W(NO)( CHC 6 H 5 )(σ-CMe 4 ) (σ- B ), respectively. For instance, the thermolysis of 1 in p -xylene affords products resulting from the activation of one and two molecules of p -xylene. The two products derived from the activation of one solvent molecule are Cp*W(NO)(CH 2 CMe 3 )(C 6 H 3 -2,5-Me 2 ) ( 10 ) and Cp*W(NO)(CH 2 CMe 3 )(CH 2 C 6 H 4 -4-Me) ( 11 ). The other two complexes derived from the activation of two solvent molecules are Cp*W(NO)(CH 2 C 6 H 4 -4-Me)(C 6 H 4 -2,5-Me 2 ) ( 12 ) and Cp*W(NO)(CH 2 C 6 H 4 -4-Me) 2 ( 13 ). The ratio of the four products in the final reaction mixture is 10: 11: 12: 13 = 1.81 ± 0.09:0.44 ± 0.05:1.0:0.15 ± 0.02. All new complexes prepared have been characterized as fully as possible by conventional spectroscopic methods, and the solid-state molecular structures of Cp*W(NO)(CH 2 C 6 H 5 )(C 6 H 3 -2,5-Me 2 ) ( 7 ) and Cp*W(NO)(CH 2 C 6 H 5 )(CH 2 C 6 H 3 -3,5-Me 2 ) ( 9 ) have been established by X-ray diffraction methods. Analyses of the product distributions resulting from the various thermolyses indicate that the benzyl products are increasingly favored over the aryl products as the number of methyl substituents on the solvent molecule increases. Likewise, the movement of the methyl groups from the ortho to meta to para position in the xylenes shifts the aryl vs benzyl product distribution toward the benzyl products. With respect to the aryl product regioselectivities, only the least sterically congested aryl regioisomers are formed in the activations of o - and m -xylene, while the meta and para aryl products are formed preferentially for α,α,α-trifluorotoluene. Finally, the distributions obtained from σ- B are more abundant in the aryl products than are those obtained from σ- A . However, despite these general trends, it is also apparent that the origin of the observed product selectivities is highly dependent on the nature of the substrate, the nature of the C−H activation products, and the intermediate alkylidene complex.
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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) | 0.001 | 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 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 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".