Tuning the Strain and Polymerizability of Organometallic Rings: The Synthesis, Structure, and Ring-Opening Polymerization Behavior of [2]Ferrocenophanes with C−Si, C−P, and C−S Bridges
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Bibliographic record
Abstract
A series of novel [2]ferrocenophanes with unsymmetrical C-E bridges has been prepared in which the covalent radius of the second-row element, E, and hence the ring strain present is varied. Species [Fe(eta-C(5)Me(4))(eta-C(5)H(4))CH(2)ER(x)] (7, ER(x) = SiMe(2); 8a, ER(x) = PPh; 8b, ER(x) = PMes; 9, ER(x) = S) were synthesized via reaction of the PMDETA (N,N,N',N' ',N' '-pentamethyldiethylenetriamine) adduct of [(eta-C(5)H(4)Li)Fe(eta-C(5)Me(4))CH(2)Li] with Cl(2)ER(x) (E = Si or P) or S(SO(2)Ph)(2). Studies of 7-9 by single-crystal X-ray diffraction confirmed the presence of ring-tilted structures: for 7, alpha (angle between the planes of the Cp rings) = 11.8(1) degrees; for 8a, alpha(average) = 14.9(3) degrees; for 8b, alpha(average) = 18.2(2) degrees; and for 9, alpha = 18.5(1) degrees. The least tilted compound, 7, was found to be resistant to thermal, anionic, and transition metal catalyzed ROP. In contrast, the significantly more tilted compounds 8a, 8b, and 9 were all found to polymerize thermally with small negative values of DeltaH(ROP) of ca. 10-20 kJ.mol(-1) determined by DSC. Whereas thermal ROP of 8a yielded the soluble high molecular weight polycarbophosphaferrocene [(eta-C(5)Me(4))Fe(eta-C(5)H(4))CH(2)PPh](n) (11), species 9 formed the insoluble polycarbothiaferrocene [(eta-C(5)Me(4))Fe(eta-C(5)H(4))CH(2)S](n) (14). Attempted anionic ROP of 8a and 9 with (n)BuLi was unsuccessful and treatment of 8a with CF(3)SO(3)Me resulted in the formation of the novel phosphonium salt [(eta-C(5)Me(4))Fe(eta-C(5)H(4))CH(2)PMePh][CF(3)SO(3)] (13), which was found to be resistant to thermal ROP as a result of its less strained structure (for 13, alpha = 11.4(7) degrees ). Treatment of 9 with CF(3)SO(3)Me or BF(3).Et(2)O resulted in the first example of cationic ROP for a transition metal-containing heterocycle to yield polycarbothiaferrocene 14. In the presence of excess 2,6-di-tert-butylpyridine as a selective proton trap, ROP of 9 was only observed with CF(3)SO(3)Me, and not BF(3).Et(2)O, which indicated that Me(+) and H(+) are the probable cationic initiators, respectively. Thermal copolymerization of 9 with trimethylene sulfide resulted in the isolation of the soluble, high molecular weight, random copolymer [(eta-C(5)Me(4))Fe(eta-C(5)H(4))CH(2)S](n)[(CH(2))(3)S](m), 15.
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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) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.002 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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 it