215033-87-7Relevant academic research and scientific papers
Facile syntheses of TiCl2(TADDOLate)(L2), efficient asymmetric ethylation of PhCHO, and an unexpected rearrangement of the tetramethyl analogue of the TADDOL ligand
Shao, Ming-Yuan,Gau, Han-Mou
, p. 4822 - 4827 (2008/10/08)
Facile syntheses of TiCl2(TADDOLate)L2 (TADDOL = α,α,α′,α′-tetraphenyl-l,3-dioxolane-4,5- dimethanol; L = THF (1), AcOEt (2)) were developed from reactions of TiCl4 with the TADDOL ligand in coordinating solvent L. The labile solvent ligands L can be replaced by a neutral bidentate ligand such as 1,2-bis(diphenylphosphino)ethane (dppe) or 3,3-dimethyl-2,4-pentanedione (diketone) to give TiCl2(TADDOLate)(L2) (L2 = dppe (3), diketone (4)). The molecular structure of complex 3 shows a structure with two chlorides in trans positions, and the dppe ligand is trans to the strong alkoxide ligands. The most significant features of the structure are the long Ti-P(phosphine) bond distances observed, indicating considerable steric hindrance arising from the TADDOLate ligand in the complex. In a reaction of the TADDOL analogue α,α,α′,α′-tetramethyl-1,3-dioxolane-4,5- dimethanol with TiCl4 in Et2O, the unexpected complex 6 derived from rearrangement of the chiral diol ligand was obtained. This rearrangement is apparently mediated by TiCl4 with the conversion of the 2,3-ketal-1,4-diol into the isomeric 3,4-ketal-1,2-diol. The asymmetric ethylations of benzaldehyde catalyzed by the complex 1, 2, or 3/Ti(O-J-Pr)4 system are efficient, and the enantioselectivities are good, with values of enantiomeric excess up to 89%.
