78791-09-0Relevant articles and documents
Catalytic and structural studies of the rhodium(I) complexes of the norphos and renorphos ligands
Kyba, Evan P.,Davis, Raymond E.,Juri, Pedro N.,Shirley, Kathleen R.
, p. 3616 - 3623 (1981)
Previously reported (-)-(R,R)-2-exo-3-endo-bis(diphenylphosphino)bicyclo[2.2.1]heptene (norphos) and its reduced congener (-)-(R,R)-2-exo-3-endo-bis(diphenylphosphino)bicyclo[2.2.1]heptane (renorphos) have been studied as chiral ligands for the Rh(I)-catalyzed reductions of prochiral substrates. It was found that reduction of the norphos to renorphos ligand occurs upon catalyst activation so that the ligand on the operating catalyst is renorphos, regardless of the precursor. High hydrogenation ee's (95%) were obtained with two enamide substrates but only moderate (63%) for itaconic acid. Crystal structure data at -100°C: a = 15.765 (8) A?, b = 20.482 (9) A?, c = 11.317 (4) A?, orthorhombic, P212121 (No. 16), Z = 4, R = 0.047, Rw = 0.048, absolute configuration determined, 3944 reflections with I > 2.5σI. X-ray data were collected at -100°C on a Syntex P21 autodiffractometer with monochromated Mo Kα radiation. The norphos ligand chelates the Rh(I) center although it must suffer severe distortions in order to do so. The largest distortion is the change in dihedral angle PCCP from 120 to 64°. The bicyclo[2.2.1]heptene skeleton absorbs this drastic change in dihedral angle in smaller changes in dihedral and bond angles, as well as bond lengths.
