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

Abstract

The synthesis of titanium(IV) Schiff base complexes has been investigated using the tetradentate salen ligand and its derivatives [L = salenH2 = 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)2TiF4] with salenH2 yields the complex [TiF4(salenH2)] 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)2TiF4] in thf. Compound 2 has been characterised by single crystal X-ray diffraction. Refluxing an equimolar ratio of salenH2 and TiCl4 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 salenH2 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 salenH2 in thf or MeCN gave the µ-oxo bridged species [TiI(salen)]2(µ-O) 6 in preference to the iodide analogue of [TiX2(salen)]. Substituted Schiff bases (MeO)2salenH2, salphenH2 and (MeO)2salphenH2 [salphenH2 = N,N′-bis(salicylidene)-1,2-phenylenediamine] react with TiCl4 (1∶1) to yield the corresponding dichloride complexes [TiCl2(L)] [L = (MeO)2salen 7, salphen 8, (MeO)2salphen 9] via the elimination of HCl. In contrast, the α-methylated salen derivative dmsalenH2 [N,N′-bis(α-methylsalicylidene)ethylenediamine] reacts in an analogous manner to the TiF4–salen system affording [TiCl4(dmsalenH2)] 10.