Comparative Density Functional Study of Associative and Dissociative Mechanisms in the Rhodium(I)-Catalyzed Olefin Hydroboration Reactions
Bibliographic record
Abstract
The [RhCl(PH 3 ) 2 ]-catalyzed hydroboration reaction C 2 H 4 + HBR 2 → H 3 CCH 2 BR 2 (R = OH, 2R = OCH CHO) was investigated by means of density functional theory type calculations using the Amsterdam density functional (ADF) program. In the first step, the borane adduct [RhCl(η 2 -HBR 2 )(PH 3 ) 2 ] ( 1 ) forms from [RhCl(PH 3 ) 2 ] and the borane HBR 2 . Subsequently, C 2 H 4 adds to 1 to give either [RhClH(BR 2 )(C 2 H 4 )(PH 3 ) 2 ] ( 2 ) ( associative pathway I ) or [RhCl(η 2 -HBR 2 )(C 2 H 4 )(PH 3 )] ( 23 ) ( dissociative pathway II ). Further branching arises because on both pathways either boron migration ( I.B, II.B ) or hydride migration ( I.H, II.H ) may occur as initial product-forming steps. It is found that the associative mechanisms, I.B and I.H, have rather similar energy profiles and the formation of product complexes [RhCl(H 3 CCH 2 BR 2 )(PH 3 ) 2 ] ( 9, 15 ) by reductive elimination requires overcoming the highest activation barriers (∼9 kcal mol - 1 ). Overall, the I.H pathway may be slightly favored over I.B for an associative mechanism. In contrast, for the dissociative mechanism migration and elimination reactions are kinetically strongly differentiated. On the II.B pathway, C−B bond formation is hindered by a high activation barrier (19.5 kcal mol - 1 ), while reductive C−H coupling furnishing the product complex [RhCl(H 3 CCH 2 BR 2 )(PH 3 )] ( 31 ) has a low barrier (6.5 kcal mol - 1 ). On the II.H pathway the reverse is found: C−H formation has a low barrier (8.4 kcal mol - 1 ), while reductive C−B formation has a high barrier (15.8 kcal mol - 1 ). In summary, the II.B pathway may be slightly more favorable for a dissociative reaction. Since side products (i.e., vinyl boranes, alkanes) are formed on the I.B and II.B pathways, we suggest that rhodium-catalyzed hydroborations are driven into a dissociative II.H reaction channel which is easier to control kinetically by using bulky electron-withdrawing phosphines as ligands in the catalyst.
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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 | 0.001 |
| 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) | 0.002 | 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 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".