DIOPHEP, a chiral diastereoisomeric bisphosphine ligand: synthesis and applications in asymmetric hydrogenations

Novel optically active diphosphine ligands, known as DIOPHEP, have been designed and synthesized starting from a derivative of tartaric acid. The ligands conjugate the sp3 chirality of the precursor of DIOP with the atropisomeric chirality of a biaryl scaffold. The stereorecognition abilities of DIOPHEP-Ru complex catalysts have been investigated in the asymmetric catalytic hydrogenation of some standard substrates suggesting a close relationship between dihedral angles and enantioselectivity.

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(−)-(S,S,Rax)DIOPHEPC43H38O4P2[α]D25=-45.0 (c 0.1, CH2Cl2)Absolute configuration: (S,S,Rax)

(+)-(S,S,Sax)DIOPHEPC43H38O4P2[α]D25=+54.5 (c 0.33, CH2Cl2)Absolute configuration: (S,S,Sax)