Titanium complexes based on chiral enantiopure dialkanolamines: synthesis, structures and catalytic activity

Abstract

New chiral enantiopure tridentate ligands (dialkanolamines) RN(CHR³CR¹R²OH)(CHR⁴CR⁵R⁶OH) 10–17 were synthesized by the opening of the epoxide ring by the action of the amines or alkanolamines. Titanium complexes, viz. [RN(CHR³CR¹R²O)(CHR⁴CR⁵R⁶O)]Ti(O-i-Pr)₂18–23 and [RN(CHR³CR¹R²O)(CHR⁴CR⁵R⁶O)]₂Ti 25–31 were synthesized by treatment of Ti(O-i-Pr)₄ with one or two equivalents of corresponding dialkanolamines. Complex (R)-PhCH(Me)N(CH₂C(Me)₂O)₂TiCl₂*HNMe₂24 was obtained from the reaction of one equivalent of dialkanolamine 10 with (Me₂N)₂TiCl₂. The composition and structure of all novel compounds were established by ¹H and ¹³C NMR spectroscopy as well as elemental analysis. The possible solution structures of 18–31 are discussed. The single-crystal X-ray diffraction study of 23, 25–28, 30, 31 indicates monomeric structures in the solid state. Chiral complexes 20, 22, 23, 25, 26, 30 were tested as chiral catalysts in the Abramov reaction and demonstrated moderate enantiomeric activity.