Stitching phospholanes together piece by piece: new modular di- and tridentate stereodirecting ligands
The modular one-pot synthesis of a large family of bi- and tridentate 2,5-dimethyl- and 2,5-diphenyl-substituted phospholanes employs air-stable chiral phospholanium chloride salts and primary amines or NH4Cl as starting materials. These were transformed into the C2-symmetric dimethyl- and diphenylp...
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| Main Authors: | , , , , |
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| Format: | Article (Journal) |
| Language: | English |
| Published: |
November 8, 2011
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| In: |
Chemistry - a European journal
Year: 2011, Volume: 17, Issue: 50, Pages: 14047-14062 |
| ISSN: | 1521-3765 |
| DOI: | 10.1002/chem.201101864 |
| Online Access: | Verlag, lizenzpflichtig, Volltext: https://doi.org/10.1002/chem.201101864 Verlag, lizenzpflichtig, Volltext: https://onlinelibrary.wiley.com/doi/abs/10.1002/chem.201101864 
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| Author Notes: | Dr. Julio Lloret Fillol, Achim Kruckenberg, Peter Scherl, Prof. Dr. Hubert Wadepohl and Prof. Dr. Lutz H. Gade |
| Summary: | The modular one-pot synthesis of a large family of bi- and tridentate 2,5-dimethyl- and 2,5-diphenyl-substituted phospholanes employs air-stable chiral phospholanium chloride salts and primary amines or NH4Cl as starting materials. These were transformed into the C2-symmetric dimethyl- and diphenylphospholane ligands, which reacted with [Rh(cod)2]BF4 (cod=1,5-cyclooctadiene) to yield the rhodium complexes [Rh(L)(cod)]BF4 (L=bisphospholane ligands). The corresponding trisphospholane complexes, 11 and 12, were obtained in high yields (81 and 92 %, respectively), and fully characterised by NMR spectroscopy, mass spectrometry and elemental analysis. Whilst in the C3-symmetric complex 11, containing the tridentate 2,5-dimethylphospholane, the ligand is bound symmetrically, different coordination behaviour was found for the diphenyl-substituted complex 12, in which the coordination of only two of the three phospholane moieties to the metal centre was observed. A DFT study at the B3PW91 level established minimum energy structures consistent with experimental findings in solution and in the solid state. The non-coordinated phospholane unit present in 12 allowed further modification of the complex through the coordination of AuIX (X=Cl, C6F5 and tris(trifluoromethyl)phenyl (FMes)) fragments to the pendant phosphane. To investigate the potential of the new ligands, the enantioselective hydrogenation of a series of prochiral olefins as benchmark substrates, using isolated Rh complexes as catalysts, was studied. The substrates included methyl esters of three dehydro-α-acetamido acids and two itaconic acid derivatives. In general good to excellent enantioselectivities (of up to >99 % ee) were observed. Ligand backbone modification by coordination of bulky AuX substituents to the free phospholane unit in complex 12 led to an outstanding enhancement of the catalyst performance and there was a clear correlation between the properties of the complex periphery and the enantioselectivity. |
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| Item Description: | Gesehen am 02.11.2022 |
| Physical Description: | Online Resource |
| ISSN: | 1521-3765 |
| DOI: | 10.1002/chem.201101864 |