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

Christian Lorber, Laure Vendier

Index: Dalton Trans. 42(34) , 12203-19, (2013)

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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), (t)Bu (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(μ(2)-NPh)3(μ(3)-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.