Titanium imido complexes utilizing orthometallated derivatized acetophenone and piperonal imine ligands: synthesis, isolation, and characterization

Abstract

A series of five ortho-lithiated imines (Li-Lⁿ; n = 1–5) was synthesized via the reaction of an aryl or alkyl acetophenone imine with n-butyllithium. The ortho-lithiated imines were subsequently reacted with Ti(NR)Cl₂py₃ (R = C(CH₃)₃, 2,6-Me₂C₆H₃, 2,6-Et₂C₆H₃, or 2,6-ⁱPr₂C₆H₃), yielding complexes of the form (Lⁿ)₂Ti(NR). Several of the resulting complexes [(L¹)₂Ti(NC(CH₃)₃), 1a; (L³)₂Ti(N-2,6-Me₂C₆H₃), 3b; and (L⁵)₂Ti(NC(CH₃)₃), 5a] were structurally characterized using small molecule X-ray diffraction. The C₂ symmetric complexes produced in these reactions displayed a distorted square pyramidal geometry. In each complex the titanium center was located above the square plane of the two coordinated bidentate ligands and the chelating C∼N ligands were folded away from the metal center. When a less sterically demanding alkylimine was used (L⁴), the resulting complex was isolated as an equilibrium mixture of cis and trans isomers of the empirical formula (L⁴)₂Ti(NC(CH₃)₃)py (cis/trans4a).