Novel aspects of the transamination reaction between Ti(NMe2)4 and primary amines

Abstract

A detailed study of the transamination reaction between Ti(NMe₂)₄ and primary amines RNH₂ is reported Alkylamines (1-adamantylamine, t-butylamine) and triphenylsilylamine yield dimers of the type [Ti(μ-NR)(NMe₂)₂]₂ (R = 1-adamantyl (1), ^tBu (2), SiPh₃ (3)). The experimental conditions and the nature of the amine are important issues that determine the scope and yield of the reaction. When reacted under the same conditions, aniline PhNH₂ does not yield the expected dimer, but instead the trimer [Ti₃(μ²-NPh)₃(μ³-NPh)(NMe₂)₄(NHMe₂)] (5) and tetramer [Ti₄(μ-NPh)₅(NMe₂)₆] (6) complexes were characterized. The reaction of Ti(NMe₂)₄ and 2,6-diisopropylaniline (Ar*NH₂) is essentially an equilibrium reaction of great complexity in which multiple species can coexist in solution. However, under certain circumstances, we were able to isolate and/or characterize several new complexes such as [Ti(μ-NAr*)(NMe₂)₂]₂ (7), [(Me₂N)₂Ti(μ-NAr*)₂Ti(NMe₂)(NHAr*)] (8), [Ti(NMe₂)₃]₂(μ-NAr*) (9), [(Ar*NH)₂Ti(μ-NAr*)₂Ti(NMe₂)₂] (10), [(Me₂N)(Me₂NH)Ti(μ-NAr*)₂Ti(NMe₂)(NAr*)] (11), Ti(NHAr*)₄ (12), and [(Ar*NH)₂Ti(μ-NAr*)₂Ti(NMe₂)(NHAr*)] (13). Complexes 8 and 11 are tautomers. Alternatively, complex 7 was prepared by deprotonation of NHMe₂ ligands in Ti(NAr*)Cl₂(NHMe₂)₂ with KN(SiMe₃)₂. Addition of pyridine (py) to the reaction of Ti(NMe₂)₄/Ar*NH₂ mixtures or to 7 or 8 allows characterization of transient [Ti(μ-NAr*)(NMe₂)₂]₂·py (14) and trapping of the intermediates [(Me₂N)(py)₂Ti(μ-NAr*)₂Ti(NMe₂)(NAr*)] (15), Ti(NAr*)(NHAr*)(NMe₂)(py)₂ (16), and Ti(NAr*)(NHAr*)₂(py)₂ (17). The crystal structures of 15 compounds were determined by X-ray diffraction studies.