Highly Active Cationic Rhodium(I) Precatalysts for the Ambient Temperature Ring-Opening Polymerization of [1]Silaferrocenophanes and Tetramethyldisilacyclobutane
Bibliographic record
Abstract
The cationic rhodium(I) complexes [Rh(1,5-cod) 2 ]A (A = OTf, PF 6, 1,5-cod = 1,5-cyclooctadiene) have been shown to exhibit high catalytic activity for the transition metal-mediated ring-opening polymerization (ROP) of silicon-bridged [1]ferrocenophanes (e.g., fcSiMe 2 ( 1a ), fc = Fe(η 5 -C 5 H 4 ) 2 ), to quantitatively afford high molecular weight ( M n > 10 5 ) polyferrocenylsilanes (e.g., [fcSiMe 2 ] n ( 2a )). However, prolonged exposure of the resulting polyferrocene solution to the catalyst resulted in a dramatic molecular weight decline. Transition metal-catalyzed ROP of tetramethyldisilacyclobutane ( 6 ) and copolymerization of this species with 1a also proved readily feasible with [Rh(1,5-cod) 2 ]OTf forming high molecular weight polycarbosilane homopolymer ( 7 ) ( M n = 4.20 × 10 5 to 1.08 × 10 6, PDI = 1.39−2.08) and poly(carbosilane- r -ferrocenylsilane) ( 8 ) copolymer ( M n = 4.63 × 10 5, PDI = 1.86), respectively. While [Rh(1,5-cod)(dmpe)]PF 6 (dmpe = bis(dimethylphosphinoethane)) proved less active as a ROP catalyst, this species represents the first phosphine-ligated catalyst for the ROP of 1a, and moreover, in this case no subsequent depolymerization of the resulting poly(ferrocenyldimethylsilane) ( 2a ) was detected. The cleavage of the polyferrocene backbone in the presence of [Rh(1,5-cod) 2 ]OTf was modeled through the catalytic reaction of Fc 2 SiMe 2 (Fc = Fe(η 5 -C 5 H 5 )(η 5 -C 5 H 4 )) with the rhodium complex (9 mol %), which resulted in Cp−Si bond cleavage affording ferrocene as the sole, isolable product. The presence of 1,5-cod inhibited the catalytic activity of both [Rh(1,5-cod) 2 ]OTf and [Rh(1,5-cod)(dmpe)]PF 6, suggesting that elimination of a 1,5-cod ligand is necessary to generate the true active catalytic species. The addition of dmpe effectively arrested the catalytic activity with [Rh(1,5-cod)(dmpe)]PF 6; this is presumably a result of the displacement of the 1,5-cod ligand by dmpe, which would generate catalytically inactive [Rh(dmpe) 2 ]PF 6 .
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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 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".