Preparations and structures of titanium(IV) complexes containing 8-hydroxyquinolinate and a Schiff-base N-(2-oxyphenyl)salicylideneiminate

In methanol, the reaction of Ti(OiPr)4, N-(2-hydroxyphenyl)salicylideneimine (H2Sap) and 8-hydroxyquinoline (HQ) in stoichiometric ratio 1:1:x yielded Ti(Sap)2 precipitate as initial product even when x was as high as 10. However, when the reaction mixture with x = 2 was left standing for 12 h or more, a small amount of red crystalline Ti(Sap)Q(OMe) was isolated. Addition of wet acetonitrile to the reaction mixture with x = 10, small amount of another red crystalline [Ti(Sap)Q]2(μ-O) was obtained after standing for 2 days. The reaction between TiQ2(OiPr)2 and H2Sap in methanol with stoichiometric ratio of y:1 also yielded Ti(Sap)2 as initial product even for y as large as 10. 1H NMR investigation of the reaction of TiQ2(OMe)2 with H2Sap revealed that Ti(Sap)Q(OMe) was not detected initially. These experimental results can be explained based on a mechanism that includes: (i) rapid reaction of H2Sap with Ti(IV) centers to form Ti(Sap)2; (ii) equilibrium between TiQ2(OMe)2 and Ti(Sap)Q(OMe); (iii) equilibrium between Ti(Sap)Q(OR) and Ti(Sap)2; and (iv) limited solubilities of Ti(Sap)Q(OR) and Ti(Sap)2. The equilibrium constants and solubilities in the mechanism were determined by the 1H NMR spectral method. The structures of Ti(Sap)Q(OMe) and [Ti(Sap)Q]2(μ-O), consisting octahedrally coordinated Ti(IV), were determined by X-ray diffraction method.

In methanol, the reactions of Ti(OiPr)4/TiQ2(OiPr)2 with Schiff-base N-(2-hydroxyphenyl)salicylideneimine (H2Sap) in the presence/absence of 8-hydroxyquinoline (HQ) yield Ti(Sap)2 initially, and Ti(Sap)Q(OMe) only after prolong standing.Figure optionsDownload as PowerPoint slide