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

The terminal formate complex [(OCHO)Ti(N3 N)] (3) containing the trianionic triamido-amine ligand (Me3 SiNCH2 CH2 )3 N3- (N3 N) was prepared via salt metathesis of [ClTi(N3 N)] (1) with sodium formate or alternatively by treatment of the alkyl complex [n BuTi(N3 N)] (2) with ammonium formate [HNEt3 ][OCHO]. Deprotonation of 3 with potassium hexamethyldisilazide gave a polymeric helical chain of the oxo complex {K[OTi(N3 N)]}n (4). Reaction of 2 with the trityl salt [Ph3 C][B(3,5-Cl2 C6 H3 )4 ] or the Brønsted acid [HNEt3 ][B(C6 F5 )4 ] gave [(Et2 O)Ti(N3 N)][BR4 ] (6[BR4 ]·Et2 O) with R = 3,5-Cl2 C6 H3 or C6 F5 . The diethyl ether ligand was easily replaced by other L-type donor ligands such as tetrahydrofuran, pyridine, and 4-dimethylaminopyridine to give 6[BR4 ]·L with L = thf, py, and dmap. Reaction of 6[BR4 ]·Et2 O with a stoichiometric amount of CO2 gave the dimeric, dicationic bis(carbamate)-bridged complexes [Ti{N(CH2 CH2 NSiMe3 )2 (CH2 CH2 NSiMe3 (μ-CO2 -ηO:ηO'))}]2 [BR4 ]2 (7[BR4 ]2 ) through insertion of one CO2 into one of the titanium-amido bonds. Addition of pyridine to 7[B(C6 F5 )4 ]2 formed the monomeric carbamate complex [(py)Ti{((O2 C-κ2 O,O')NSiMe3 CH2 CH2 )N(CH2 CH2 NSiMe3 )2 }][B(C6 F5 )4 ] (8[B(C6 F5 )4 ]·py). The cationic formate-bridged species [(Ti(N3 N))2 (μ-OCHO-ηO:ηO')][BR4 ] (10[BR4 ]) readily formed when the terminal formate complex 3 was reacted with the cationic 6[BR4 ]. The reactivity of triamido-amine stabilized titanium(iv) complexes is shown to differ considerably from that of related titanium tris(anilide) complexes.