Reactions of Bis(pentafluorophenyl)borane with Cp<sub>2</sub>Ta(CH<sub>2</sub>)CH<sub>3</sub>: Generation and Trapping of Tantalocene Borataalkene Complexes
Bibliographic record
Abstract
Reaction of Cp 2 Ta( CH 2 ) 3 with 2 equiv of HB(C 6 F 5 ) 2 results in production of the dihydride Cp 2 Ta(CH 2 B(C 6 F 5 ) 2 )(μ-H)(H), 1, plus 1 equiv of H 3 CB(C 6 F 5 ) 2 . The pathway to 1 involves stepwise attack of borane first at the methylene group, followed by attack at the methyl group, which undergoes alkyl/hydride exchange with the second equivalent of HB(C 6 F 5 ) 2 . The product of HB(C 6 F 5 ) 2 addition to the methylene ligand, methyl hydride complex Cp 2 Ta(CH 2 B(C 6 F 5 ) 2 )(μ-H)(CH 3 ), 2, can be intercepted by carrying out the reaction in hexane at low temperature, a medium in which it is nearly totally insoluble. This complex eliminates methane at higher temperatures in a first-order decomposition process (Δ H ⧧ = 20.4(5) kcal mol - 1 and Δ S ⧧ = −2.0(2) cal mol - 1 K - 1 ). The product, a borataalkene complex formulated as Cp 2 Ta[CH 2 B(C 6 F 5 ) 2 ], 3, is unstable and cannot be isolated. DFT calculations support its formulation and show that it is present as a singlet/triplet mixture, accounting for the observed paramagnetism of solutions containing 3 . While 3 cannot be isolated or spectroscopically probed, it can be trapped if 2 is allowed to decompose in the presence of t BuNC or CO, giving the products Cp 2 Ta[η 2 -CH 2 B(C 6 F 5 ) 2 ](L) (L = t BuNC, 4; CO, 5 ). Both of these compounds have been structurally characterized, and the structural and spectroscopic data for these compounds support an η 2 bonding description for the borataalkene ligand which is reminiscent of the commonly held Dewar−Chatt−Duncanson model for alkene bonding to transition metals. DFT calculations on 5 and the model complex Cp 2 Ta[η 2 -CH 2 BH 2 ](CO), 6, provide further support for this description. The facile conversion of this ligand from an η 2 to an η 1 bonding mode is proposed to account for some H/D exchange processes observed in both dihydride 1 and methyl hydride complex 2 . Plausible mechanisms for both of these processes are proposed.
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) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.002 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 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".