0000000000116631
AUTHOR
Sabine Verch
Optically active titanium complexes containing a tridentate linked amido-cyclopentadienyl ligand
Optically active titanium complexes Ti{η5:η1-C5R4SiMe2NC6H10 (OCH2Ph)-2}Cl2 (R = H, Me), containing a cyclopentadienyl ligand linked to the chiral trans-2-benzyloxycyclohexylamido group, were synthesized and characterized in both enantiomerically pure forms. A single crystal X-ray structure analysis of (−)-(R,R)-Ti{η5:η1-C5H4SiMe2NC6H10(OCH2Ph)-2}Cl2 shows a structure in which the benzyloxy group in the amido sidechain is not interacting with the titanium center. Upon activation with n-butyllithium, these complexes hydrogenate acetophenone N-benzylimine with low enantioselectivity. Chirality 12:472–475, 2000. © 2000 Wiley-Liss, Inc.
Optically Active Titanium Complexes Containing Linked Amido‐cyclopentadienyl Ligands: Their Use as Asymmetric Hydrogenation Catalysts
Optically active titanium complexes of the formula Ti(η5:η1−C5R4SiMe2NCHMePh)Cl2 (R = H, Me), containing the cyclopentadienyl ligand linked to a chiral 1-phenylethylamido moiety, were synthesized and characterized in both enantiomerically pure forms. A single-crystal X-ray structural analysis of (S)()Ti(η5:η1−C5H4SiMe2NCHMePh)Cl2 shows a conformation in which the phenyl group is turned away from the metal center. NOE measurements suggest that a related structure is retained in solution. Upon activation with n-butyllithium, these complexes show hydrogenation activity toward imines with slight enantioselectivity.
Chiral complexes of titanium containing a linked amido-cyclopentadienyl ligand: synthesis, structure, and asymmetric imine hydrogenation catalysis
Abstract A series of mono- and disubstituted derivatives (−)-(S)-Ti(η5:η1-C5Me4SiMe2NCHMePh)(X)Cl (X=CH2SiMe3, BH4) and (−)-(S)-Ti(η5:η1-C5Me4SiMe2NCHMePh)X2 (X=OSO2CF3, OiPr, Me, CH2Ph) was prepared from (−)-(S)-Ti(η5:η1-C5Me4SiMe2NCHMePh)Cl2 without significant racemization at the stereogenic center. The monosubstituted complexes are formed as mixtures of diastereomers. One diastereomeric monoalkyl (STi, SC)-Ti(η5:η1-C5Me4SiMe2NCHMePh)(CH2SiMe3)Cl was characterized by X-ray single crystal structure analysis. When the (−)-(S)-NCHMePh group is attached to planar chiral ring moieties 3-tBuC5H3, C9H6, and C9H5(SiMe3)-3 and coordinated at the titanium center, diastereomeric mixtures are formed…