Direct Detection of 1,1-Diphenyl-2-neopentylsilene and the Effects of Solvent Polarity on Its Reactivity with Nucleophiles
Bibliographic record
Abstract
The reactivity of the transient silene 1,1-diphenyl-2-neopentylsilene ( 4 ) has been studied in various solvents by laser flash photolysis methods, using trans -1,1,3,3-tetraphenyl-2,4-dineopentyl-1,3-disilacyclobutane as the precursor. Silene 4 exhibits a lifetime of ca. 250 μs and a UV absorption maximum of λ max = 335 nm (ε = 10000 ± 2900 M - 1 cm - 1 ) in dry, deoxygenated hexane, where it undergoes head-to-tail dimerization and reacts with oxygen with absolute rate constants of k dim = (5 ± 2) × 10 8 M - 1 s - 1 and k O2 = (6.5 ± 0.8) × 10 5 M - 1 s - 1, respectively. Identical absorption maxima are exhibited by 4 in 1,2-dichloroethane, tetrahydrofuran, and acetonitrile solution, indicating that the silene does not form detectable Lewis acid−base complexes with these solvents, thus making it possible to study the effects of solvent polarity on silene reactivity for the first time. Accordingly, absolute rate constants for reaction of 4 with acetone, methanol, acetic acid, 2,2,2-trifluoroethanol, and n -butylamine have been determined as a function of temperature in two or more of the four solvents. The results are compared to previously reported data for 1,1-diphenylsilene ( 2a ) and show that the 2-neopentyl substituent in 4 enhances the reactivity of the Si C bond with oxygen, but reduces its reactivity with nucleophilic reagents and toward [2+2]-dimerization by as much as a factor of 10 3 . As with 2a, the Arrhenius parameters for the reactions of 4 are consistent with stepwise mechanisms, initiated by reversible complexation between the nucleophile and the silene, followed by H-transfer. The absolute rate constants at 25 °C vary by only a factor of 3−10 with solvent in each case, but there is a general trend toward increasingly positive Arrhenius activation energies and pre-exponential factors with increasing solvent polarity. The mechanistic ramifications of these results are discussed.
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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) | 0.001 | 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".