[25483-56-1] · C13H33N3Ti · Methyltitanium Tris(diethylamide) · (MW 279.37)
(thermally stable reagent useful for alkylative amination of carbonyl compounds2)
Physical Data: mp 5 °C.
Solubility: sol Et2O.
Form Supplied in: not available commercially.
Analysis of Reagent Purity: 1H NMR in C6D6: 3.71 (q, 12H); 1.25 (t, 18H); 0.43 (s, 3H).
Preparative Methods: a solution of Methyllithium (or Methylmagnesium Bromide) in Et2O is added slowly to a stirred equimolar solution of Chlorotris(diethylamino)titanium3 or BrTi(NEt2)3 in Et2O at -30 °C. After 0.5 h at -30 °C and 1 h at rt, the yellow solution can be used as is2,4 or can be isolated5 by sublimation at 60-70 °C/0.001 mmHg.
Handling, Storage, and Precautions: moisture sensitive; thermally stable.
The use of titanium compounds as components of Ziegler-Natta polymerization catalysts1b,1c has led to the preparation of numerous organotitanium derivatives that have found other synthetic applications as well.1d Among the various titanium ligands the dialkylamido groups produce the least acidic and most thermally stable organotitanium species, presumably due to stronger electron donation and larger steric hindrance. Thus, while Methyltitanium Trichloride and Methyltitanium Triisopropoxide decompose at rt over several hours, MeTi(NEt2)3 is thermally stable at rt and decomposes at temperatures above 120 °C.6
Nonenolizable aldehydes react with MeTi(NEt2)3 to give tertiary amines through the addition of both the methyl group and one of the NEt2 ligands. The reaction works in moderate yields with aliphatic (eq 1),2 aromatic, and a,b-unsaturated aldehydes (eq 2).2 The reaction proceeds via the initial addition of the amino group to the carbonyl, followed by the formation of an iminium intermediate which undergoes nucleophilic attack by the methyl group. The yields are lowered by a competitive formation of diamine or enamine products (with enolizable aldehydes). Both of these hydrolyze back to the starting material during the acidic aqueous workup.
This reaction also works with the corresponding perfluoroalkyl derivatives (eq 3).7
Unlike MeTiCl3 and MeTi(O-i-Pr)3, which carry out Grignard-type additions to aldehydes and ketones, MeTi(NEt2)3 is not suitable for this type of reaction since the diethylamide group adds to the carbonyl faster than the methyl group. However, with RTi(NEt2)3 derivatives of more reactive carbon nucleophiles, such as CH2=CHCH2Ti(NEt2)3, the carbonyl additions can be efficient (eq 4).4
Nicos A. Petasis & Irini Akritopoulou-Zanze
University of Southern California, Los Angeles, CA, USA