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)
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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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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 | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.002 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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.
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