A General Decomposition Pathway for Phosphine-Stabilized Metathesis Catalysts: Lewis Donors Accelerate Methylidene Abstraction
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Bibliographic record
Abstract
High Resolution Image Download MS PowerPoint Slide Sterically accessible Lewis donors are shown to accelerate decomposition during catalysis, for a broad range of Grubbs-class metathesis catalysts. These include benzylidene derivatives RuCl 2 (NHC)(PCy 3 )(═CHPh) ( Ru-2: NHC = H 2 IMes, a; IMes, b; H 2 IPr, c; IPr, d; H 2 ITol, e ) and indenylidene complexes RuCl 2 (NHC)(PCy 3 )(═C 15 H 10 ) (NHC = H 2 IMes, Ru-2f; IMes, Ru-2g ). All of these precatalysts form methylidene complex RuCl 2 (NHC)(═CH 2 ) Ru-3 as the active species in metathesis of terminal olefins, and generate RuCl 2 (NHC)(PCy 3 )(═CH 2 ) Ru-4 as the catalyst resting state. On treatment with a 10-fold excess of pyridine, Ru-4a and Ru-4b decomposed within minutes in solution at RT, eliminating [MePCy 3 ]Cl A by net loss of three ligands (PCy 3, methylidene, and one chloride), and a mesityl proton. In comparison, loss of A from Ru-4a in the absence of a donor requires up to 3 days at 55 °C. The σ-alkyl intermediate RuCl 2 ( 13 CH 2 PCy 3 )(NHC) (py) 2 resulting from nucleophilic attack of free PCy 3 on the methylidene ligand was undetectable for the H 2 IMes system, but was spectroscopically observable for the IMes system. The relevance of this pathway to decomposition of catalysts Ru-2a – g was demonstrated by assessing the impact of pyridine on the in situ-generated methylidene species. Slow initiation (as observed for the indenylidene catalysts) did not protect against methylidene abstraction. Importantly, studies with Ru-4a and Ru-4b indicated that weaker donors (THF, MeCN, DMSO, MeOH, and even H 2 O) likewise promote this pathway, at rates that increase with donor concentration, and severely degrade catalyst productivity in RCM, even for a readily cyclized substrate. In all cases, A was the sole or major 31 P-containing decomposition product. For DMSO, a first-order dependence of decomposition rates on DMSO concentration was established. This behavior sends a warning about the use of phosphine-stabilized metathesis catalysts in donor solvents, or with substrates bearing readily accessible donor sites. Addition of pyridine to RuCl 2 (H 2 IMes)(PCy 3 )(═CHMe) did not result in ethylidene abstraction, indicating that this decomposition pathway can be inhibited by use of substrates in which the olefin bears a β-methyl group.
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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 | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 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