Meta-Substituted Thienyl Benzenes: A Comparative Synthetic, Structural and Computational Study
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Bibliographic record
Abstract
A selection of metal-catalyzed C-C bond-forming strategies has been evaluated in the synthesis of a series of meta-substituted thienylbenzenes, (T(n))(2)C(6)H(4) and (T(n))(3)C(6)H(3) (n = 1, 2; T(1) = 2-thienyl; T(2) = 2,2'-bithien-5-yl). Kumada coupling reactions catalyzed by PdCl(2)(dppf) between the appropriate thienyl Grignard and either 1,3- or 1,3,5-bromo- or iodobenzenes were found to be the most reliable in terms of convenience, selectivity and yield (dppf = 1,1'-bis(diphenylphosphino)ferrocene). These conditions also allowed the optimized syntheses of mixed (thienyl)(halo)benzenes, (T(n))C(6)H(3)X(2) and (T(n))(2)C(6)H(3)X (X = Br, I); the latter bromides could be further elaborated in subsequent Stille, Sonogashira, or Kumada reactions to furnish bis(thienyl) compounds bearing electron-donating or -withdrawing groups in the third meta position, (T(n))(2)C(6)H(3)R (R = Ph, p-MeOC(6)H(4), p-FC(6)H(4); n = 1, 2) and (T(1))(2)C(6)H(3)R' (R' = Me, C[triple bond]CPh, Fc; Fc = ferrocenyl). The relative effects of R, R', and n were evaluated by electronic spectroscopy, cyclic voltammetry and calculation. The absorption and emission characteristics and calculated ionization potentials and HOMO-LUMO gaps of these compounds were strongly dependent on n and largely insensitive to R/R'. These measured and calculated properties were also found to be largely invariant with respect to the degree of substitution about the central ring in the meta-substituted benzenes (T(n))(m)X(3-m)C(6)H(3) (m = 1-3; n = 1, 2; X = Br, H), although in the case of n = 1, there was a smooth, albeit small, increase in the emission maximum with increasing thienyl substitution. These findings essentially confirmed earlier theoretical predictions that the thienyl "arms" of meta-substituted phenyl-cored dendrimers were predominantly responsible for absorption and that excitons were localized to the "arms" without any electronic coupling between them, but also introduced the caveat that there was a minimum of two contiguous thiophene rings required for strict exciton localization to the arms. The oxidation potentials of the compounds in solution ranged from 0.9 to 1.6 V and were not rationally dependent on the degree of substitution or the nature of R/R'.
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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 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.012 | 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