Formation of Triple-Stranded Dinuclear Helicates with Dicatecholimine Ligands: The Influence of Steric Hindrance at the Spacer

A series of new imine‐bridged dicatechol ligands 3a–f‐H4 with sterically demanding groups at the spacers are used for the formation of titanium(IV) complexes M4[(3)3Ti2]. All three ligands 3a–c‐H4 form triple‐stranded dinuclear helicates. When the bulky ligands 3a‐H4 or 3c‐H4 are used with potassium as the countercation, oligomeric or polymeric side products are also observed. The imine‐bridged ligand 3e‐H4 quantitatively forms helicates M4[(3e)3Ti2] and not a M4L6 tetrahedron as observed with Raymond’s analogous amide‐bridged dicatechol ligand 3i‐H4. NMR spectroscopic investigations at variable temperature show that ligand 3f‐H4, which possesses a spiro fluorenyl group at the central unit of the spacer, forms the meso‐helicate M4[(3f)3Ti2]. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)