Kinetic and Mechanistic Studies of the Formal (1+2)- and (1+4)-Cycloadditions of Germylenes to Conjugated Dienes
Bibliographic record
Abstract
Fast kinetic studies of the reactions of isoprene and 2,3-dimethyl-1,3-butadiene (DMB) with diphenylgermylene (GePh 2, 2a ) and of isoprene with a series of diarylgermylenes bearing polar ring substituents (GeAr 2, 2b − g ) have been carried out in hexanes solution. Though the major stable products of the reactions with isoprene are the corresponding 1,1-diarylgermacyclopent-3-ene derivatives, the results indicate that the major initial products are the corresponding transient 1,1-diaryl-2-vinylgermiranes ( 6a − g ) resulting from formal (1+2)-cycloaddition to the less-substituted C═C bond of the diene. These compounds are formed reversibly and with rate constants in excess of 10 9 M −1 s −1, and appear as discrete reaction intermediates exhibiting λ max = 285 nm and lifetimes of 2−670 μs depending on the identity of the germylene and the diene. The variations in the lifetimes with aryl substituents are shown to be most consistent with a stepwise mechanism for vinylgermirane → germacyclopent-3-ene isomerization, involving (reversible) dissociation to the free germylene and diene followed by (irreversible) (1+4)-cycloaddition. The bimolecular rate constants for (1+4)-cycloaddition to isoprene, calculated from the data on the basis of this model, vary over the range of 5 × 10 6 to 3 × 10 8 M −1 s −1 depending on the aryl ring substituent(s). The variation in the rate and equilibrium constants for reaction of 2a − g with isoprene indicates that the germylene plays the role of an electrophile in both the (1+2)- and (1+4)-cycloaddition processes and demands the involvement of a polarized steady-state intermediate in the (1+2)-addition reaction. The temperature dependence of the experimental rate and equilibrium constants for reaction of GePh 2 with isoprene, and of the rate coefficient for decay of the corresponding vinylgermirane, allows most aspects of the potential energy surface to be defined quantitatively.
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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 | 0.001 |
| 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 | 0.001 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 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".