Ortho-Selective C−H Activation of Substituted Benzenes Effected by a Tungsten Alkylidene Complex without Substituent Coordination
Bibliographic record
Abstract
Gentle thermolysis of the bis(neopentyl) complex Cp*W(NO)(CH 2 CMe 3 ) 2 ( 1 ) at 70 °C in various substituted benzenes results in the loss of neopentane and the generation of the transient alkylidene complex Cp*W(NO)( CHCMe 3 ) ( A ), which subsequently effects single C−H bond activations of the benzenes. These activations exhibit a pronounced selectivity for the C−H linkages ortho to the benzene substituents. Thus, thermal reactions of 1 with C 6 H 5 X lead to the preferential formation of the corresponding Cp*W(NO)(CH 2 CMe 3 )( o -C 6 H 4 X) complexes, the ortho-selectivity, i.e., X = F > OMe > Cl > Br > C⋮CPh, diminishing as the steric demands of the substituents increase. Consistently, thermolyses of 1 in o -C 6 H 4 X 2 afford Cp*W(NO)(CH 2 CMe 3 )(2,3-C 6 H 3 X 2 ) complexes with 98% selectivity when X = F and 82% selectivity when X = Cl. Similarly, the principal organometallic products resulting from the thermolyses of 1 in m -C 6 H 4 X 2 are the ortho-para-activated isomers Cp*W(NO)(CH 2 CMe 3 )(2,4-C 6 H 3 X 2 ) with 84% selectivity when X = F and 89% selectivity when X = Cl. Finally, thermolyses of 1 in para-disubstituted benzenes p -C 6 H 4 XY (X = F or OMe, Y = Cl or OMe) again reveal that the ortho-directing abilities of the substituents diminish in the order F > OMe > Cl. Some mechanistic insights into these activation processes have been obtained by monitoring of the early stages of the thermolysis of 1 in chlorobenzene by 1 H NMR spectroscopy. This monitoring reveals that the selectivity of the alkylidene intermediate A for forming the ortho-activated isomer is thermodynamic rather than kinetic in nature. Thus, the meta- and para-activated isomers are formed initially, but then convert to the ortho-activated product. The principal organometallic complexes resulting from ortho-C−H activations are formally 16-electron species in which there are no interactions between the tungsten centers and the Lewis-basic benzene substituents. Instead, the Lewis-acidic tungsten centers engage in intramolecular agostic interactions with the methylene C−H bonds of their neopentyl ligands to acquire some additional electron density. Being coordinatively and electronically unsaturated, these tungsten complexes react readily with added Lewis bases. Thus, treatment of Cp*W(NO)(CH 2 CMe 3 )( o -C 6 H 4 F) with Et 4 NCN and CO produces [Et 4 N] + [Cp*W(NO)(CH 2 CMe 3 )(CN)( o -C 6 H 4 F)] - and Cp*W(NO)(η 2 -C( O)CH 2 CMe 3 )( o -C 6 H 4 F), respectively, and the solid-state molecular structure of the latter complex has also been established by a single-crystal X-ray crystallographic analysis.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| 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) | 0.008 | 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".