Formate complexes of titanium(iv) supported by a triamido-amine ligand.

The terminal formate complex [(OCHO)Ti(NN)] (3) containing the trianionic triamido-amine ligand (MeSiNCHCH)N (NN) was prepared via salt metathesis of [ClTi(NN)] (1) with sodium formate or alternatively by treatment of the alkyl complex [BuTi(NN)] (2) with ammonium formate [HNEt][OCHO]. Deprotonation of 3 with potassium hexamethyldisilazide gave a polymeric helical chain of the oxo complex {K[OTi(NN)]} (4). Reaction of 2 with the trityl salt [PhC][B(3,5-ClCH)] or the Brønsted acid [HNEt][B(CF)] gave [(EtO)Ti(NN)][BR] (6[BR]·EtO) with R = 3,5-ClCH or CF. The diethyl ether ligand was easily replaced by other L-type donor ligands such as tetrahydrofuran, pyridine, and 4-dimethylaminopyridine to give 6[BR]·L with L = thf, py, and dmap. Reaction of 6[BR]·EtO with a stoichiometric amount of CO gave the dimeric, dicationic bis(carbamate)-bridged complexes [Ti{N(CHCHNSiMe)(CHCHNSiMe(μ-CO-ηO:ηO'))}][BR] (7[BR]) through insertion of one CO into one of the titanium-amido bonds. Addition of pyridine to 7[B(CF)] formed the monomeric carbamate complex [(py)Ti{((OC-κO,O')NSiMeCHCH)N(CHCHNSiMe)}][B(CF)] (8[B(CF)]·py). The cationic formate-bridged species [(Ti(NN))(μ-OCHO-ηO:ηO')][BR] (10[BR]) readily formed when the terminal formate complex 3 was reacted with the cationic 6[BR]. The reactivity of triamido-amine stabilized titanium(iv) complexes is shown to differ considerably from that of related titanium tris(anilide) complexes.