Effect of Azide and Chloride Binding to Diamino-bis(phenolate) Chromium Complexes on CO<sub>2</sub>/Cyclohexene Oxide Copolymerization
Bibliographic record
Abstract
The affinity for nucleophile (azide, N 3 –, and chloride, Cl – ) binding significantly influences the catalytic activity of chromium complexes for the copolymerization of cyclohexene oxide (CHO) and CO 2 . The binding of N 3 – and Cl – to two amino-bis(phenolate) Cr(III) chloride complexes [ L1 Cr(μ-Cl)] 2 ( 1 ) and [ L2 CrCl(THF)] ( 2·THF ), where L1 = methoxyethylamino- N, N -bis(2-methylene-4,6-di- tert -butylphenolate) and L2 = dimethylaminoethylamino- N, N -bis(2-methylene-4,6-di- tert -butylphenolate), were studied by both matrix assisted laser desorption/ionization time-of-flight and electrospray ionization mass spectrometry (MALDI-TOF-MS and ESI-MS, respectively). Upon reaction with [PPN][N 3 ] ([PPN] = bis(triphenylphosphine)iminium), 1 exhibited greater ability to form six-coordinate bis-azide ions [ L1 Cr(N 3 ) 2 ] − and produced fewer five-coordinate species detected by MS than 2·THF . This corresponded to 2·THF having a significantly faster rate of polymerization with anionic nucleophile cocatalysts than 1 . In the presence of 1 equiv of [PPN][N 3 ], 1 showed a slow reaction rate with an induction period of 20 min, whereas 2·THF showed a much faster reaction rate with no induction period. Also, 1 in the presence of 1 equiv of [PPN][Cl] showed faster copolymerization than in the presence of 2 equiv of [PPN][Cl]. The binding of chloride to 1 from addition of [PPN][Cl] was studied by UV–vis spectroscopy, which showed an equilibrium constant of 1.6 × 10 3 M –1 favoring the formation of [ L1 Cr(Cl) 2 ] − . The ring-opening process of CHO was observed in the mixture of 2·THF /CHO/[PPN][N 3 ] via ESI-MS. Combined with MALDI-TOF-MS of the polymer product obtained within the first 60 min, it was shown that N 3 – preferentially initiates ring-opening of the epoxide in CHO. Upon consumption of N 3 – through generation of active polymer chains, the chloride originating from the metal complex can serve as initiator of epoxide ring-opening. This was confirmed by the occurrence of chloride-containing polymers later in the reaction. Taken together, these studies provide mechanistic insight into the copolymerization of CO 2 and epoxide by diamino-bis(phenolate) Cr(III) chloride complexes.
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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) | 0.000 | 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) | 0.002 | 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".