Chiral complexes of titanium containing a linked amido-cyclopentadienyl ligand: synthesis, structure, and asymmetric imine hydrogenation catalysis

A series of mono- and disubstituted derivatives (-)-(S)-Ti(eta(5):eta(1)-C5 Me4SiMe2NCHMePh)(X)Cl (X = CH2SiMe3, BH4) and (-)-(S)-Ti(eta(5):eta(1)-C5Me 4SiMe2NCHMePh)X-2 (X = OSO2CF3, OiPr, Me, CH2Ph) was prepared from (-)-(S)- Ti(eta(5):eta(1)-C5Me4SiMe2NCHMePh)Cl-2 without significant racemization at the stereogenic center. The monosubstituted complexes are formed as mixtur es of diastereomers. One diastereomeric monoalkyl (S-Ti, S-C)-Ti(eta(5):eta (1)-C5Me4SiMe2NCHMePh)(CH2SiMe3)Cl was characterized by X-ray single crysta l structure analysis. When the (-)-(S)-NCHMePh group is attached to planar chiral ring moieties 3-'BuC5H3, C9H6, and C9H5(SiMe3)-3 and coordinated at the titanium center, diastereomeric mixtures are formed. A series of titani um complexes Ti(eta(5):eta(1)-C5R4SiMe2NR')Cl-2 (R = H, Me; R' = CHMeC10H7, CHMeCMe3, CHPhCMe3, CHMeC6H11, (1S)-pinanyl-3, (1R)-bornyl-2) containing a n enantiomerically pure linked amido-cyclopentadienyl ligands were synthesi zed and characterized by H-1- and C-13-NMR spectroscopy, mass spectrometry, and elemental analysis. The crystal structure of a three-legged piano-stoo l molecule was determined for (+)-(1S)-Ti(eta(5):eta(1)-C(5)Me(4)SiMe(2)NCH (2)pinanyl-3)Cl-2 by a single-crystal X-ray diffraction study. Upon activat ion with n-butyllithium a selection of these dichloro complexes catalyzed t he hydrogenation of acetophenone N-benzylimine with good conversions for R = H, but with low enantioselectivities. (C) 2000 Elsevier Science S.A. All rights reserved.