Binuclear Activation of Cumulenes: Roles of the Adjacent Metals and the Cumulene Binding Mode in the Activation Process
Bibliographic record
Abstract
The binuclear complex [Ir 2 (CH 3 )(CO)(μ-CO)(dppm) 2 ][CF 3 SO 3 ] ( 1; dppm = μ-Ph 2 PCH 2 PPh 2 ) reacts with allene and methylallene to ultimately yield the vinylcarbene products [Ir 2 H(CO) 2 (μ-η 1:η 3 -HCC(CH 3 )C(H)R)(dppm) 2 ][CF 3 SO 3 ] (R = H ( 6 ), CH 3 ( 7 )). Monitoring the reactions by NMR spectroscopy ( 1 H, 13 C, 31 P) between −78 °C and ambient temperature allows the observation of several intermediates in each of these transformations in which the allene moves from an η 2 binding site on one metal, through an η 1:η 1 -bridging geometry in which the cumulene is coordinated through the “H 2 C C” moiety, to an η 1:η 3 -bridging geometry in which the central carbon of the cumulene is σ-bound to one metal, adjacent to the methyl ligand, while the three cumulene carbons are η 3 -bound to the adjacent metal. We propose that formation of the respective vinyl carbene products results from migration of the methyl ligand to the central cumulene carbon followed by activation of a cumulene C−H bond. 1,1-Dimethylallene reacts with 1 at −78 °C to yield a methylene hydride product containing an η 2 -bound cumulene on one metal, much as observed for the first products in the allene and methylallene reactions. Upon warming, this intermediate isomerizes to the final product containing a methyl ligand on one metal and an η 2 -bound cumulene on the other. No cumulene-bridged products are observed with this disubstituted allene. 1,1-Difluoroallene also yields a methylene hydride product at −78 °C, which is analogous to the first species observed in all cases noted above. In this case, warming results in movement of the cumulene to an η 1:η 1 -bridging position in which this group binds to the metals via the “H 2 C C” moiety. Unlike the transformations observed with allene and methyl allene, difluoroallene undergoes no additional transformations as the temperature is raised. A rationalization of these transformations is presented together with a perspective on how the cumulene ligand moves over the dimetallic framework leading to the final products.
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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 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.003 | 0.001 |
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".