Premium
Catalytic and Structural Features of Hydroxy and Methoxy Groups as Hemilabile Coordinating Ligands in Chiral (Diphosphane)rhodium(I) Hydrogenation Catalysts
Author(s) -
Borns Susanne,
Kadyrov Renat,
Heller Detlef,
Baumann Wolfgang,
Spannenberg Anke,
Kempe Rhett,
Holz Jens,
Börner Armin
Publication year - 1998
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/(sici)1099-0682(199809)1998:9<1291::aid-ejic1291>3.0.co;2-l
Subject(s) - chemistry , rhodium , catalysis , ligand (biochemistry) , chelation , ether , medicinal chemistry , asymmetric hydrogenation , oxygen atom , butane , stereochemistry , metal , group (periodic table) , polymer chemistry , organic chemistry , molecule , enantioselective synthesis , receptor , biochemistry
The influence of two threo ‐arranged methoxy or hydroxy groups as hemilabile ligands in seven‐membered (diphosphane)Rh I chelates upon the asymmetric hydrogenation is studied. In comparison to the parent complex based on 1,4‐bis(diphenylphosphanyl)butane (DPPB) a lowering of the reaction rate is caused by the hemilabile ligands. The catalyst bearing the hydroxy groups gives significantly higher enantioselectivities than the corresponding methoxy complex (by ca. 35 % ee). X‐ray structural analysis reveals that the oxygen atom of the hydroxy group is by 0.9 Å closer to the metal center than that of the methyl ether. 31 P‐NMR studies give evidence that the dihydroxy diphosphane ligand binds at low temperature exclusively in the η 3 ‐coordination mode, whereas for the dimethoxy complex also an η 2 ‐coordinated isomer can be found. These differences in complexation could be responsible for the superior enantioselectivities achieved with this and other hydroxy catalysts.