Salophan complexes of group IV metals

The coordination chemistry of tetradentate Salophan ligands with titanium and zirconium alkoxides is described for the first time. Three new Salophan ligand precursors featuring different phenolate substituents (ortho-Me, ortho,para-di-Cl, ortho,para-di-tBu) were synthesized in addition to the known prototypical Salophan precursor, by a sequence of condensation and reduction. All ligand precursors were reacted with the metal alkoxides Ti(OiPr)₄ and Zr(OtBu)₄. The unsubstituted Salophan led to a complex product mixture for both titanium and zirconium. The methyl-substituted ligand led to a clean complex only with zirconium, and the other ligands gave well-defined coordination chemistry with both metals. NMR analysis indicated that these Salophans acted as dianionic ligands, giving rise to hexa-coordinate complexes of C₂-symmetry. X-ray analysis of three complexes supported this view, and revealed that the ligands wrapping mode was fac-fac and that the orientation of the labile groups was cis. A partial hydrolysis of one of the titanium complexes led to a dinuclear bridging oxo complex in which the ligand wrapping mode had changed to fac-mer, as revealed from its crystal structure.