Journal
EUROPEAN JOURNAL OF ORGANIC CHEMISTRY
Volume 2021, Issue 17, Pages 2367-2374Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/ejoc.202100109
Keywords
Asymmetric catalysis; Chiral tetraphosphane; D-2 symmetry; Homogeneous hydrogenation; Rhodium complexes
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PHANE-TetraPHOS, a novel D-2 symmetric tetraphosphane, features four homotopic diphenylphosphane groups with indistinguishable spatial arrangement. Enantiomeric purity was achieved through crystallization and alkaline treatment, leading to enantiopure PHANE-TetraPHOS antipodes. These ligands showed comparable catalytic activity and enantiodiscrimination ability to PHANEPHOS, using only half the amount of chiral ligand.
PHANE-TetraPHOS, a new D-2 symmetric tetraphosphane based on the [2.2]paracyclophane scaffold, has been synthesized and characterized. The peculiarity of this system is the presence of four homotopic diphenylphosphane groups, exchangeable through C-2 symmetry operations and consequently indistinguishable. Their spatial arrangement allows the simultaneous complexation of two metal atoms. Enantiomeric purity was attained at tetra-phosphane oxide level by fractional crystallization of the diastereomeric adducts obtained from the racemate with enantiopure dibenzoyltartaric acids. Alkaline treatment of diastereomerically pure adducts followed by exhaustive P-O groups reduction with HSiCl3 gave both PHANE-TetraPHOS antipodes in an enantiopure state. They were tested as rhodium ligands in the homogeneous enantioselective hydrogenation of some benchmark unsaturated compounds. Catalytic activity and enantiodiscrimination ability were found comparable to those exhibited by the complexes of the parent bidentate ligand PHANEPHOS, but only half a mole of precious chiral ligand was employed.
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