Theoretical and Synthetic Investigations of Carbodiimide Insertions into Al−CH<sub>3</sub> and Al−N(CH<sub>3</sub>)<sub>2</sub> Bonds
Bibliographic record
Abstract
Carbodiimides are known to insert into aluminum-carbon bonds to form four-membered bidentate amidinate chelate rings. Insertions into Al-R and Al-NR'2 (R, R' = alkyl) have been reported in the literature. We have devised a mechanism for these insertions and modeled it using density functional theory (DFT) calculations. The calculated barrier heights for competitive insertions show the insertion into Al-N(CH3)2 goes through a lower barrier than the reaction with Al-CH3 for diisopropyl carbodiimide due to the necessity of forming a pentavalent carbon intermediate in the Al-CH3 case. However, insertion into Al-CH3 has the lower barrier for the reaction with di-tert-butyl carbodiimide because of steric effects, which is consistent with the published experimental results. We have synthesized aluminum amidinates containing two and three acetamidinate rings via insertion of 2 and 3 equiv of diisopropylcarbodiimide into trimethylaluminum (TMA). The crystal structure for [CH3C(N(i)Pr)2]2 AlCH3 is reported. We have found that, although the first insertion is rapid at room temperature, the second and third insertions require refluxing above 70 degrees C. We have calculated the barrier heights for the first and second insertion and have found that this is due to a higher barrier for the migration of the methyl group in the second insertion. This higher barrier is the result of the lack of an exergic precoordination of the carbodiimide to the metal center, which facilitates the first insertion.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.001 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.004 | 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".