Intermolecular C−H Activation of Hydrocarbons by Tungsten Alkylidene Complexes: An Experimental and Computational Mechanistic Study
Bibliographic record
Abstract
Cp*W(NO)(CH 2 CMe 3 ) 2 ( 1 ) and Cp*W(NO)(CH 2 CMe 3 )(CH 2 C 6 H 5 ) ( 2 ) under moderate conditions (70 °C, 40 h) generate the reactive complexes Cp*W(NO)( CHCMe 3 ) ( A ) and Cp*W(NO)( CHC 6 H 5 ) ( B ), respectively, which activate hydrocarbon solvents via the addition of C−H across the M C bond. The α-deuterated derivative Cp*W(NO)(CD 2 CMe 3 ) 2 ( 1- d 4 ) undergoes intramolecular H/D exchange within the neopentyl ligands, consistent with the formation of σ-neopentane complexes prior to neopentane elimination. The thermolysis of 1 in a 1:1 molar mixture of tetramethylsilane- h 12 and tetramethylsilane- d 12 (70 °C, 40 h) yields an intermolecular KIE of 1.07(4):1. Thermolysis of 1 and 2 in 1:1 benzene/benzene- d 6 yields intermolecular KIEs of 1.03(5):1 and 1.17(19):1, respectively. The KIE values are inconsistent with rate-determining C−H bond addition to the M C linkage and indicate that coordination of the substrate to the metal center is the discriminating factor in alkane and arene intermolecular competitions. The complexes Cp*W(NO)(CH 2 CMe 3 )(C 6 D 5 ) ( 5- d 5 ) and Cp*W(NO)(CH 2 C 6 H 5 )(C 6 D 5 ) ( 6- d 5 ) convert to the respective H/D scrambled products Cp*W(NO)(CHD syn CMe 3 )(C 6 D 4 H 1 ) ( 5 ‘ - d 5 ) and Cp*W(NO)(CHD syn C 6 H 5 )(C 6 D 4 H 1 ) ( 6 ‘ - d 5 ) under thermolytic conditions, consistent with the occurrence of reversible aromatic sp 2 C−H bond cleavage. The results suggest that the previously reported discrimination between the aryl and benzyl products of toluene activation by A and B originates from coordination of toluene to the metal center in two distinct modes. Supporting DFT calculations on the activation of toluene by CpW(NO)( CH 2 ) ( C ) indicate that aromatic sp 2 C−H bond activation proceeds through a π-arene complex, while benzylic sp 3 C−H bond activation proceeds through a η 2 ( C, H ),σ-phenylmethane complex. The principal factor behind the preferential formation of the aryl products appears to be the relative energies of formation of these intermediates.
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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) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 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".