Routes to New N-Heterocyclic Carbene Titanium(IV) Imido Complexes

Mono-N-heterocyclic carbene (NHC) complex TiCl2(NMe2)2(IMes) (1) (IMes = 1,3-dimesitylimidazol-2-ylidene) has been prepared through the addition of the free carbene to TiCl2(NMe2)2. This procedure affords 1 in higher yield than the previously reported synthesis of 1 that consists in reacting Ti(NMe2)4 with 2 equiv of the imidazolium IMes·HCl and that in some cases we demonstrated affords 1 with concomitant formation of the titanium(III) bis-NHC complex TiCl2(NMe2)(IMes)2 (2). Compound 1 reacts with primary amines to give compounds of the type Ti(NR)Cl2(NHMe2)(IMes) (3). Alternatively, complexes 3 could be prepared from imido precursors Ti(NR)Cl2(NHMe2)2 and IMes, whereas the pyridine adducts Ti(NR)Cl2(Py)3 produced Ti(NR)Cl2(Py)(IMes) (6). The reaction between dimeric complexes [Ti(μ-NAr)(NMe2)2]2 (Ar = 2,6-Pri2-C6H3 and 2,6-Cl2-C6H3) and the salt IMes·HCl gives incomplete conversions into Ti(NAr)Cl2(NHMe2)(IMes) with formation of two side products when Ar = 2,6-Cl2-C6H3, formulated as Ti(NAr)Cl2(IMes)2 (4) and Ti(NAr)Cl(NHAr)(NHMe2)(IMes) (5). X-ray studies were carried out for 1, 2, 3a, 3d, 3e, 4, and 5.