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 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) | 0.002 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.002 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.003 | 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".