4,4′-Biphenolate complexes of titanium and zirconium

4,4'-Biphenolate ligands (R4BIPOH2) bearing methyl or tert-butyl substituents in the 3,3',5,5'-positions participate in alcoholysis reactions with metal precursors, including TiCl4, Ti(O(i)Pr)4 and Cp2MCl2. The tetra-tert-butyl derivative shows evidence of an intermediate monotitanium species (Bu4BIPOH)Ti(O(i)Pr)3 during titrations of the ligand with Ti(O(i)Pr)4, while (Bu4BIPO)(Ti(O(i)Pr)3)2 exists as a simple monomeric molecule in solution. (Me4BIPO)(Ti(O(i)Pr)3)2 shows evidence of aggregation into oligomeric species in solution, although its insolubility hampered the complete characterization of these species. A reaction between the d(l) complex TiCl3(THF)3 and 3,3',5,5'-(t)Bu4-4,4'-biphenoquinone produced (Bu4BIPO)[TiCl3(THF)]2, while direct reactions between TiCl4 and Bu4BIPOH2 in toluene resulted in the isolation of the dealkylated product, (Bu2BIPO)[TiCl3(Et2O)]2 (where the (t)Bu groups occur in the 3,3'-positions), after treatment with ether. Refluxing Me4BIPOH2 and Cp2MCl2 (M = Ti or Zr) in toluene produced bismetallocene chloride complexes.