Transition Metal-Catalyzed Formation of Phosphorus−Boron Bonds: A New Route to Phosphinoborane Rings, Chains, and Macromolecules
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Bibliographic record
Abstract
A novel catalytic dehydrocoupling route for the synthesis of linear, cyclic, and polymeric phosphinoboranes has been developed. The dehydrocoupling of neat Ph 2 PH·BH 3, which is otherwise very slow below 170 °C, is catalyzed by [{Rh(μ-Cl)(1,5-cod)} 2 ] or [Rh(1,5-cod) 2 ][OTf] (0.5−1 mol % Rh) to give the linear compound Ph 2 PH−BH 2 −PPh 2 −BH 3 ( 1 ) at 90 °C, and a mixture of the cyclic trimer [Ph 2 P−BH 2 ] 3 ( 2a ) and tetramer [Ph 2 P−BH 2 ] 4 ( 2b ) at 120 °C. In addition, the catalytic potential of other (e.g., Ti, Ru, Rh, Ir, Pd, Pt) complexes toward the dehydrocoupling of Ph 2 PH·BH 3 was investigated and was in many cases demonstrated. The molecular structures of 1 and 2b, and of the primary phosphine−borane adduct PhPH 2 ·BH 3, were determined by single-crystal X-ray analysis. The dehydrogenative coupling of PhPH 2 ·BH 3 gave low-molecular-weight poly(phenylphosphinoborane) [PhPH−BH 2 ] n ( 3 ) when performed in toluene (110 °C) with ca. 0.5 mol % [Rh(1,5-cod) 2 ][OTf] as catalyst. The absolute weight-average molecular weight was determined by static light scattering (SLS) in THF which showed that M w = 5600. Samples of high-molecular-weight polymer 3 ( M w = 31 000 or 33 300 by SLS) were synthesized using neat conditions at 90−130 °C in the presence of [{Rh(μ-Cl)(1,5-cod)} 2 ], anhydrous RhCl 3, or RhCl 3 hydrate (ca. 1 mol % Rh). Poly(phosphinoborane) 3 was thereby obtained in ca. 75% yield as an air-stable, off-white solid and was structurally characterized by 1 H, 11 B, 13 C, and 31 P NMR and IR spectroscopy and elemental analysis. The hydrodynamic diameters for polymers 3 in THF were also determined by dynamic light scattering (DLS). Catalytic dehydrocoupling of the alkyl-substituted phosphine−borane adduct i BuPH 2 ·BH 3 was also investigated and was found to be much slower than that of PhPH 2 ·BH 3 . This produced poly(isobutylphosphinoborane) [ i BuPH−BH 2 ] n ( 4 ) under neat conditions at 120 °C in the presence of [{Rh(μ-Cl)(1,5-cod)} 2 ] in 80% yield. Multinuclear NMR spectroscopy and DLS were also used to characterize polymer 4, and the latter indicated that M w = ca. 10 000−20 000. Prolonged heating of polymers 3 and 4 at elevated temperatures in the presence of catalyst led to insoluble but solvent-swellable gels possibly due to light interchain cross-linking through P−B bonds. In the absence of rhodium catalyst thermally induced dehydrocoupling of PhPH 2 ·BH 3 and i BuPH 2 ·BH 3 proceeds very slowly and forms only low-molecular-weight materials with complex NMR spectra and which probably possess a branched structure.
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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 | 0.000 |
| 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