Chiral titanium hydride complexes

D. Reduction of Imines with Hydrogen in the Presence of a Chiral Titanium Hydride Complex... 

Chiral titanium complexes are also employed as effective asymmetric catalysts for other carbon-carbon bond-forming reactions, for example addition of diketene (Sch. 66) [154c,162], Friedel-Crafts reaction (Sch. 67) [163] (Sch. 68) [164], iodocar-bocyclization (Sch. 69) [165], Torgov cyclization (Sch. 70) [166], and [2 -i- 1] cycloaddition (Sch. 71) [167]. Asymmetric functional group transformations can also be catalyzed by chiral titanium complexes. These transformations, for example the Sharpless oxidation [168] or hydride reduction [169] are, however, beyond the scope of this review because of space limitations. Representative results are, therefore, covered by the reference list. 

The in situ formed basic cyclopentadienyl complex of titanium, ethylene-bis( f-tetrahydroindenyl)-titanium hydride (EBTHI)TiH) containing a planar element of chirality, is active for the reduction of a C=N double bond of both N-aryl-imines (Schiff bases) and unsubstituted imines (108,109). (EBTHl)TiX2 derivatives are used as precursors of the hydride analogue. The chiral zirconium analogues of the above-mentioned complexes provided a breakthrough in asymmetric polymerization of terminal oleflns (110). 

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