Electronic and Steric Effects on the Lewis Acidities of Transient Silylenes and Germylenes: Equilibrium Constants for Complexation with Chalcogen and Pnictogen Donors
Bibliographic record
Abstract
The Lewis acid–base complexation reactions of dimethyl-, diphenyl-, and dimesitylsilylene (SiMe 2, SiPh 2, and SiMes 2, respectively) and their germanium homologues (GeMe 2, GePh 2, and GeMes 2 ) with diethyl ether (Et 2 O), tetrahydrothiophene (THT), triethylphosphine (Et 3 P), and tricyclohexylphosphine (Cy 3 P) have been characterized in hydrocarbon solvents at 25 °C by laser flash photolysis methods. Together with previously reported (and some new) data for the complexation of the six transient tetrellylenes with methanol (MeOH), tetrahydrofuran (THF), and di- and triethylamine (Et 2 NH and Et 3 N, respectively), the results allow the first systematic assessment of the thermodynamics of Lewis acid–base complexation of simple dialkyl- and diarylsilylenes and their germanium homologues with chalcogen and pnictogen donors in solution. The equilibrium constants ( K C ) for complexation of the six species with Et 2 O span a range of ca. 10 5 M –1, decreasing in the order SiPh 2 > SiMe 2 > GePh 2 > GeMe 2 ≫ SiMes 2 > GeMes 2 . For each homologous MR 2 pair, K C is consistently 10–40 times larger for the silylene than the germylene, indicating a systematic difference in binding free energy of 1.5–2.2 kcal mol –1 . Equilibrium constants have been determined for complexation of SiMes 2 and GeMes 2 with all the donors in the series except Et 3 P, for which only a lower limit can be determined. Those for SiMes 2 decrease in the order Et 3 P > Cy 3 P > Et 2 NH > THT > Et 3 N > THF > Et 2 O; GeMes 2 is consistently less acidic, but its binding constants follow a similar ordering. The experimental data are supplemented with theoretical (Gaussian-4) calculations of thermochemical parameters for the complexation of SiMe 2 and GeMe 2 with 17 O, S, N, and P donors, which are shown to agree with experiment to within 1 kcal mol –1 for the 6 systems that have also been studied experimentally. The calculations confirm that, in general, trialkylphosphines bind most strongly, followed by amines, sulfides, and then ethers and alcohols. SiMe 2 and GeMe 2 are borderline-soft Lewis acids, stronger and softer than trimethylborane in both cases.
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How this classification was reachedexpand
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) | 0.000 | 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) | 0.000 | 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 itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, 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".