Density Functional Study of the Migratory Insertion Step in the Carbonylation of Methanol Catalyzed by [M(CO)<sub>2</sub>I<sub>2</sub>]<sup>-</sup>(M = Rh, Ir)
Bibliographic record
Abstract
Quantum-mechanical calculations based on density functional theory (DFT) have been carried out on the migratory insertion process [M(CO) 2 I 3 (CH 3 )] - → [M(CO)I 3 (COCH 3 )] - (M = Rh, Ir), which represents an important step in methanol carbonylation. The calculated free energies of activation (Δ G ⧧ ) are 27.7 kcal mol - 1 (Ir) and 17.2 kcal mol - 1 (Rh), in good agreement with the experimental estimates at 30.6 ± 1.0 kcal mol - 1 (Ir) and 19.3 ± 0.5 kcal mol - 1 (Rh). The higher barrier for M = Ir is attributed to a relativistic stabilization of the Ir−CH 3 bond. It is indicated that enthalpic and entropic contributions to Δ G ⧧ can vary considerably, depending on reaction conditions, without changing Δ G ⧧ considerably. Especially, simulations based on ab initio molecular dynamics (AIMD) underlined that the reaction system might prefer to trade entropy for enthalpy in polar solutions by dissociating an I - ligand for M = Ir. A systematic study was also carried out on the general methyl migration reaction [Ir(CO) 2 I 2 L(CH 3 )] n - → [Ir(CO)I 2 L(COCH 3 )] n - ( n = 0, 1), in which an iodide ligand trans to methyl is replaced by another ligand L (where L = CH 3 OH, CH 3 C(O)OH, CO, P(OCH 3 ) 3, SnI 3 - ) or an empty coordination site. The free energy of activation for the methyl migration in [Ir(CO) 2 I 2 L(CH 3 )] with L trans to methyl follows the order P(OCH 3 ) 3 > CO > SnI 3 -, none > I - > CH 3 OH, CH 3 C(O)OH with respect to the ligand L. This order is to a first approximation determined by the ability of L to labilize the M−CH 3 bond trans to it. The order is further shaped by the ability of the π-acceptors L = CO, P(OCH 3 ) 3 to stabilize the transition state, and, in the case of L = none, by the relocation of an iodide ligand to the site trans to the migrating methyl group. It is finally discussed how placing L cis to the migrating CH 3 group might influence the migratory aptitude of methyl.
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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 | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| 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".