Selective Ring-Opening Reactions of [1]Ferrocenophanes with Boron Halides: A Novel Route to Functionalized Ferrocenylboranes and Boron-Containing Oligo- and Poly(ferrocene)s
Bibliographic record
Abstract
The reactivity of strained [1]ferrocenophanes, [Fe(eta-C5H4)2ERx] (ERx = SiMe2, 1a: SiMePh, 1b; SnR2, 1c), towards boron halides has been investigated and has been shown to provide a facile pathway to ferrocene derivatives functionalized with Lewis acidic boron centers. The boron halides RBX2 (R = Cl, Ph, fc; X = Cl, Br) (fc = Fe(eta-C5H4)2) lead to selective cleavage of the Si-Cp bonds in 1a and 1b to give, depending on the reaction stoichiometry, functionalized mono- or diferrocenylboranes RnB [(eta-C5H4)Fe(eta-C5H4SiMe2Cl)](3-n) (2a: R = Cl, n = 2; 2b: R = Cl, n = 1; 2c: R = Ph, n = 1) and RnB[(eta-C5H4)Fe(eta-C5H4SiMePhCl)](3-n) (2d: R = Cl, n = 2) in high yields. Compounds 2a-d were characterized by multinuclear NMR spectroscopy, mass spectrometry, and by single-crystal X-ray diffraction (for 2b). Most likely due to steric constraints, a triferrocenylborane was not obtained even from the reaction of BCl3 with an excess of 1a, whereas facile formation of the diferrocenylphenylborane 2c from PhBCl2 and two equivalents of 1a was observed. Selective hydrolysis of the B-Cl bonds of chlorodiferrocenylborane 2b in the presence of trace amounts of water led to the silylated tetranuclear ferrocene complex [(ClMe2Sifc)2B-O-B(fcSiMe2Cl)2] (3) without cleavage of the Si-Cl bonds. The structure of 3 was confirmed by an X-ray diffraction study. Studies of the reactivity of the higher Group 14 homologue of 1a and 1b, the tin-bridged [1]ferrocenophane 1c, revealed that facile addition of B-Cl bonds occurs across the Sn-Cp bonds to yield the 1-stannyl-1'-borylferrocenes [(ClMes2Sn)fc(BClR)] (4a: R = Cl; 4b: R = Ph; Mes = 2,4,6-Me3C6H2). The new synthetic methodology can be extended to bifunctional Lewis acids such as the bis(boryl)ferrocene 1,1'-fc(BBr2)2, which affords the linear boron-bridged ferrocene trimer 1,1'-[fc[B(Br)fcSiMe2Br]2] 5 in 54% isolated yield. In order to incorporate the functionalized ferrocenylboranes into polymer structures, compound 2c was reduced with Li[BEt3H] to give the silicon-hydride functionalized species [PhB[(eta-C5H4)Fe(eta-C5H4SiMe2H)]2] (6), which was then used as a capping reagent in the transition metal catalyzed polymerization of 1a. This process leads to the incorporation of the ferrocenylborane unit into the main chain of a poly(ferrocenylsilane) to afford [PhB-[(fcSiMe2)(n-1)fcSiMe2H]2] (7).
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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) | 0.001 | 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 | 0.001 |
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".