Insights into the Intermolecular C–H Activations of Hydrocarbons Initiated by Cp*W(NO)(η<sup>3</sup>-allyl)(CH<sub>2</sub>CMe<sub>3</sub>) Complexes
Bibliographic record
Abstract
Thermolyses of 18e Cp*W(NO)(η 3 -allyl)(CH 2 CMe 3 ) compounds (Cp* = η 5 -C 5 Me 5 ) result in the intramolecular elimination of CMe 4 and the formation of 16e η 2 -diene and/or η 2 -allene intermediate complexes that effect a variety of intermolecular C–H activations of hydrocarbons. The outcomes of the reactions of the Cp*W(NO)(η 3 -allyl)(CH 2 CMe 3 ) compounds with both C(sp 3 )–H and C(sp 2 )–H bonds of hydrocarbons are dependent on the natures of the allyl ligands in ways that are not immediately obvious. In an effort to better understand the different selectivities of the various C–H activation processes, we have examined several of these transformations by DFT calculations. The results of these computational investigations have provided several interesting and useful insights into the mechanistic pathways involved. Specifically, they have established that geminal dialkyl substituents on the allyl ligands markedly stabilize the η 2 -allene intermediate complexes, whereas the absence of such substituents favors the formation of the η 2 -diene complexes. In the case of the analogous molybdenum systems, the η 2 -diene intermediate complexes undergo rapid isomerization to the η 4 -diene complexes and do not effect intermolecular C–H activations. In some instances involving the tungsten complexes, the initially formed η 1 -hydrocarbyl product (which may or may not be isolable) isomerizes by intramolecular exchange of the newly formed hydrocarbyl ligand with a hydrogen atom on the allyl ligand or undergoes additional C–H activations and is converted to a new hydrido allyl compound. DFT methods indicate that a plausible mechanism for the latter transformation involves a β-hydrogen abstraction from the lateral alkyl chain by the allyl ligand. The rate-determining step of this process is thus the formation of a 16e η 2 -olefin complex with the olefin originating from the alkyl chain, and this process should be favored by relatively electron-rich Cp*W(NO)(η 3 -allyl)( n -alkyl) complexes, as is experimentally observed. In all cases of benzene C(sp 2 )–H activations by the tungsten systems, the η 2 -allene intermediate complexes exhibit better reactivity than the η 2 -diene intermediates. However, theoretical considerations indicate that the stereochemical properties of the first-formed Cp*W(NO)(η 3 -allyl)(Ph) products determine their differing thermal stabilities. If the aryl–allyl coupling product, Cp*W(NO)(η 2 -allyl-Ph), contains an activatable C–H bond close to the tungsten center, then the thermodynamically favored intramolecular exchange of the phenyl ligand with a hydrogen atom on the allyl ligand occurs. Otherwise, it does not, and the Cp*W(NO)(η 3 -allyl)(Ph) complexes persist.
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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 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.004 | 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".