Direct Detection of Wiberg's Silene (1,1-Dimethyl-2,2-bis(trimethylsilyl)silene) and Absolute Rate Constants for Its Reactions in Solution
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Bibliographic record
Abstract
Photolysis of (pentamethyldisilanyl)(trimethylsilyl)diazomethane ( 6a ) and the analogous ketene derivative ( 6b ) in hydrocarbon solution in the presence of aliphatic alcohols affords alkoxysilanes from trapping of four isomeric silene reactive intermediates, in yields of ca. 78%, 6%, 9%, and 8%, respectively. Nanosecond laser flash photolysis (193 or 248 nm) of 6a, b allows detection of two transient species, the most prominent of which has been assigned as 1,1-dimethyl-2,2-bis(trimethylsilyl)silene ( 3; λ max ∼265 nm). The second species exhibits λ max = 310 nm and much lower reactivity toward alcohols and is consistent with any of E -1,2-dimethyl-1,2-bis(trimethylsilyl)silene ( E - 9 ), the corresponding Z -isomer ( Z - 9 ), or 1,2,2-trimethyl-2-pentamethyldisilanylsilene ( 8g ). The four silenes are the products expected from the various possible 1,2-migrations in the carbene intermediate formed by photoextrusion of nitrogen or carbon monoxide from the precursors. Absolute rate constants for reaction of 3 and 9 ( 8g ) with methanol, methanol- Od, 2-propanol, cyclohexanol, tert -butyl alcohol, tert -butylamine, and acetic acid have been determined in hexane solution at 24 °C. In all cases but one, the ratios of the rate constants (relative to tert -butyl alcohol) for reaction of silene 3 compare favorably with the relative rate data reported previously for this silene in diethyl ether solution at 100 °C. The rate constant for addition of methanol to 3 in hexane at 25 °C correlates with those of a series of C-substituted 1,1-dimethylsilenes and indicates this silene to be the most highly electrophilic derivative known. The rates exhibit a bell-shaped dependence on temperature over the 0−60 °C range and a maximum at 24 °C, consistent with a stepwise mechanism for reaction with methanol. The transient UV spectra and reactivity observed in THF solution at 24 °C indicate that 3 complexes strongly with the ether solvent, resulting in 10 3 - to 10 4 -fold reductions in its reactivity toward aliphatic alcohols compared to hexane solution. Smaller (ca. 20-fold) reductions in reactivity are observed for the minor silene product(s) under the same conditions.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| 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) | 0.000 | 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