Halide titanium(IV) Schiff base complexes; fluoride and bromide derivatives and evidence for a new seven-coordinate chloride intermediate

The synthesis of titanium(IV) Schiff base complexes has been investigated using the tetradentate salen ligand and its derivatives [L = salenH(2) = N,N'-bis(salicylidene)ethylenediamine]. Complexes of the form [TiX2(L)], [(thf)TiX2(L)] and [TiX4(LH2)] have been observed with the nature of these products being dependent on the salen derivative, halide and reaction condition employed. The reaction of [(thf)(2)TiF4] with salenH(2) yields the complex [TiF4(salenH(2))] 1 which does not eliminate HF to form [TiF2(salen)] 2 even after toluene reflux. Compound 2 can be obtained in 90% yield using the silylated Schiff base salen(TMS)(2) (TMS = Me3Si) and [(thf)(2)TiF4] in thf. Compound 2 has been characterised by single crystal X-ray diffraction. Refluxing an equimolar ratio of salenH(2) and TlCl4 gave the previously prepared [TiCl2(salen)] 3, while stirring the same reactants at room temperature afforded the seven-coordinate solvent adduct [(thf)TiCl2(salen)] 4 in quantitative yield. TiBr4 reacts similarly with salenH(2) or salen(TMS)(2) to give [TiBr2(salen)] 5. The bromide analogue of 4 was identified from its characteristic FAB(+) mass spectrum. Reaction of TiI4 with salen(TMS)(2) or salenH(2) in thf or MeCN gave the mu-oxo bridged species [TiI(salen)](2)(mu-O) 6 in preference to the iodide analogue of [TiX2(salen)]. Substituted Schiff bases (MeO)(2)salenH(2), salphenH(2) and (MeO)(2)salphenH(2) [salphenH(2) = N,N'-bis(salicylidene)-1,2-phenylenediamine] react with TiCl4 (1 : 1) to yield the corresponding dichloride complexes [TiCl2(L)] [L = (MeO)(2)salen 7, salphen 8, (MeO)(2)salphen 9] via the elimination of HCl. In contrast, the alpha-methylated salen derivative dmsalenH(2) [N,N'-bis(alpha-methylsalicylidene)ethylenediamine] reacts in an analogous manner to the TiF4-salen system affording [TiCl4(dmsalenH(2))] 10.