Competitive ArC−H and ArC−X (X = Cl, Br) Activation in Halobenzenes at Cationic Titanium Centers
Bibliographic record
Abstract
The titanium methyl cation [Cp*((tBu3P=N)TiCH3]+ [B(C6F5)4]- reacts rapidly with H2 to give the analogous cationic hydride [Cp*((tBu3P=N)TiH(THF)n]+ [B(C6F5)4]- (n = 0, 1), which can be trapped and isolated as its THF adduct 1 x THF (n = 1). When generated in the presence of chloro or bromobenzene, 1 undergoes C-X activation or ortho-C-H activation, depending on the amount of dihydrogen present in the reaction medium. At approximately 4 atm of H2, C-X activation is preferred, giving the halocations [Cp*((tBu3P= N)TiX]+ [B(C6F5)4]- (2X) and C6H6/biphenyl mixtures. At lower pressures of H2 (>1 atm), the beta-halophenyl cations [Cp*((tBu3P=N)Ti(2-X-C6H4)]+ [B(C6F5)4]- (3X) are the products isolated. In the absence of H2, these compounds are quite thermally stable, but undergo beta-halogen elimination upon moderate heating, to give 2X (approximately 20%) and compounds 4X which are the result of reaction between 2X and benzyne via addition of the benzyne C-C triple bond across the Ti-N bond of the phosphinimide ligand. Thus, three separate bond activation processes are operative in this system: direct C-X activation, ortho-C-H activation, and indirect C-X activation via beta-halogen elimination. Mechanistic studies on all three processes have been done and support a radical pathway for direct C-X cleavage, sigma-bond metathesis of the ortho-C-H bond of eta(1)-coordinated C6H5X, and beta-halogen elimination from base-free compound 3X.
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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".