Frustrated Lewis pairs derived from N-heterocyclic carbenes and Lewis acids
Bibliographic record
Abstract
The chemistry of frustrated Lewis pairs derived from N-heterocyclic carbenes and a number of Lewis acids has been probed. The combination of 1,3-bis[2,6-(di-iso-propyl)phenyl]-1,3-imidazol-2-ylidene (IDipp) (1) with B(C6F5)3 was shown to give the classical Lewis acid-base adduct (IDipp)B(C6F5)3 (2) which was unreactive. In contrast, the combination 1,3-di-tert-butyl-1,3-imidazol-2-ylidene (3) with B(C6F5)3 proved to form a frustrated Lewis pair, and reacts with H2 to give the salt [ItBuH][HB(C6F5)3] (4) in high yield. In a similar fashion, addition of (3) to a series of amine-borane adducts including H3NB(C6F5)3 (5), PhH2NB(C6F5)3 (6) and PhH2NB(C6F5)3 (7) led to deprotonation and formation of imidazolium amido-borate salts [ItBuH][H2NB(C6F5)3] (8), [ItBuH][PhHNB(C6F5)3] (9) and [ItBuH][Ph2NB(C6F5)3] (10). Similar reactions of the amine-borane adducts EtNH2B(C6F5)3 (11) tBuNH2B(C6F5)3 (12) and Et2NHB(C6F5)3 (13) gave the amidoboranes EtHNB(C6F5)2 (14) tBuHNB(C6F5)2 (15) and Et2NB(C6F5)2 (16) respectively, with liberation of C6F5H and an equivalent of unreacted carbene. Mechanistically these reactions are thought to proceed through transient imidazolium salts similar to (8)-(10). In addition, the combination of carbene (3) and the cation [CPh3]+ in frustrated Lewis pair chemistry has been probed. Reaction of this combination at room temperature results in the immediate formation of [C3H2N2tBu2(C6H5)CPh2][B(C6F5)4] (17) stemming from carbene attack at a para-carbon of one of the phenyl rings of trityl. Addition of carbene to the benzyl amine adduct of [CPh3][B(C6F5)4] results in the formation of [ItBuH][B(C6F5)4] (18) and the secondary amine Ph3CNHCH2Ph (19), thus providing the first example of an all carbon-based frustrated Lewis pair. Crystallographic data for (2), (4), (9) and (13) are reported.
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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 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".