Isocyanide insertion reactions into the TaC bonds of cationic and zwitterionic tantalocenes
Bibliographic record
Abstract
The insertion of isonitriles R' NC (R' = t-Bu, C 6 H 11 , CH 2 C 6 H 5 ) occurs exclusively into the TaCH 2 bonds of the zwitterionic compounds (C 5 H 4 R) 2 Ta[CH 2 B(C 6 F 5 ) 3 ]CH 3 (R = H, 1a; R = CH 3 , 1b) at relatively slow rates at room temperature to form N-out isomers as the sole kinetic products. By comparison, insertion of the same isonitrile substrates into a TaCH 3 bond of the non-zwitterionic analogs [(C 5 H 4 R) 2 Ta(CH 3 ) 2 ][A] (R = H, A = B(C 6 F 5 ) 4 , 3a; R = CH 3 , A = BF 4 , 3b) occurs much more rapidly, again to form N-out isomers exclusively under kinetic conditions. The difference in rate is attributed to the presence of a ground state α-agostic interaction in the zwitterionic compounds, which is not featured in the dimethyl ion pairs. All of the N-out isomers formed undergo thermal and irreversible conversion to the corresponding N-in isomers at rates that are conveniently followed by 1 H NMR spectroscopy. The rates were studied at different temperatures to obtain activation parameters for each transformation. The rate and activation trends for this isomerization were analyzed as a function of the structural changes in the compounds. It was found that the rate decreased as the steric bulk of the isonitrile substitutent R' increased and that the rates were faster for the series that incorporated the more electron-donating C 5 H 4 CH 3 ancillary ligand. Furthermore, isomerization rates for the zwitterionic N-out compounds were faster than those found in the non-zwitterionic series. This study represents one of the more extensive kinetic analyses of the rate of N-out to N-in isomerization as a function of structural changes. The observations are consistent with the mechanistic picture that has been developed for this process, involving dissociation of the η 2 iminoacyl ligand, rotation about the MC iminoacyl bond and recoordination to the inside site of the metallocene wedge. Key words: cationic metallocenes, isocyanide insertion, agostic interactions, tantalum.
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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) | 0.005 | 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".