Formate complexes of tri- and tetravalent titanium supported by a tris(phenolato)amine ligand.

Titanium(III) and titanium(IV) formate complexes supported by the sterically encumbering tris(phenolato)amine ligand (H(ON) = tris(4,6-di--butyl-2-hydroxybenzyl)amine) are described. Salt metathesis of the chlorido precursor [(ON)TiCl] (1-Cl) with sodium formate in a 2 : 1 ratio in THF gave a dimer of sodium dititanium triformate units with 12-membered ring [Na{(ON)Ti}(μ-OCHO-η:η')] (3-Na) when crystallized from acetonitrile. Complex 3-Na was also prepared by reacting the previously reported terminal formate complex [(ON)Ti(OCHO)] (2) with excess sodium formate. Salt metathesis of 1-Cl with potassium formate gave a tetratitanium cluster of the composition [K{(ON)Ti}(OCHO)] (3-K) which can be also obtained by treating 2 with potassium formate. In 3-K both Ti and K centers are six-coordinate. The titanium(III) complexes [(ON)Ti(L)] (4-L, L = THF, THP, EtO) and solvent free dimeric [(ON)Ti] (5) were synthesized by reduction of 1-Cl with sodium sand or magnesium in THF, THP, EtO, and -pentane, respectively. The -butyl formate adduct of titanium(III)-[(ON)Ti(BuOCHO)] (6) was isolated by reacting 4-L or 5 with -butyl formate. Complex 6 is thermolabile and slowly decomposed in solution to produce a formate-bridged mixed-valence titanium(III)/titanium(IV) complex [{(ON)Ti}(μ-OCHO-η:η')] (7) which further decomposed to a mixture containing 2, [(ON)Ti(OH)] and [(ON)Ti-O-Ti(ON)]. All new complexes were isolated in moderate to good yields and fully characterized by elemental analysis, H and C NMR spectroscopy, and single crystal X-ray diffraction analysis. For the titanium(III) complexes solution magnetic moments were measured by the Evans method and EPR spectra recorded as toluene glass at 77 K.