Comparative Studies of Thermally Induced Homolytic CarbonCarbon Bond Cleavage Reactions of Strained Dicarba[2]ferrocenophanes and Their Ring‐Opened Oligomers and Polymers
Bibliographic record
Abstract
Reactivity studies of dicarba[2]ferrocenophanes and also their corresponding ring-opened oligomers and polymers have been conducted in order to provide mechanistic insight into the processes that occur under the conditions of their thermal ring-opening polymerisation (ROP) (300 °C). Thermolysis of dicarba[2]ferrocenophane rac-[Fe(η(5)-C5H4)2(CHPh)2] (rac-14; 300 °C, 1 h) does not lead to thermal ROP. To investigate this system further, rac-14 was heated in the presence of an excess of cyclopentadienyl anion, to mimic the postulated propagating sites for thermally polymerisable analogues. This afforded acyclic [(η(5)-C5H5)Fe(η(5)-C5H4)-CH2Ph] (17) through cleavage of both a Fe-Cp bond and also the C-C bond derived from the dicarba bridge. Evidence supporting a potential homolytic C-C bond cleavage pathway that occurs in the absence of ring-strain was provided through thermolysis of an acyclic analogue of rac-14, namely [(η(5)-C5H5)Fe(η(5)-C5H4)(CHPh)2-C5H5] (15; 300 °C, 1 h), which also afforded ferrocene derivative 17. This reactivity pathway appears general for post-ROP species bearing phenyl substituents on adjacent carbons, and consequently was also observed during the thermolysis of linear polyferrocenylethylene [Fe(η(5)-C5H4)2(CHPh)2]n (16; 300 °C, 1 h), which was prepared by photocontrolled ROP of rac-14 at 5 °C. This afforded ferrocene derivative [Fe(η(5)-C5H4CH2Ph)2] (23) through selective cleavage of the -H(Ph)C-C(Ph)H- bonds in the dicarba linkers. These processes appear to be facilitated by the presence of bulky, radical-stabilising phenyl substituents on each carbon of the linker, as demonstrated through the contrasting thermal properties of unsubstituted linear trimer [(η(5)-C5H5)Fe(η(5)-C5H4)(CH2)2(η(5)-C5H4)Fe(η(5)-C5H4)(CH2)2(η(5)-C5H4)Fe(η(5)-C5H5)] (29) with a -H2 C-CH2- spacer, which proved significantly more stable under analogous conditions. Evidence for the radical intermediates formed through C-C bond cleavage was detected through high-resolution mass spectrometric analysis of co-thermolysis reactions involving rac-14 and 15 (300 °C, 1 h), which indicated the presence of higher molecular weight species, postulated to be formed through cross-coupling of these intermediates.
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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) | 0.002 | 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 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".