Anionic π-Bonded Derivatives of Titanium(IV)

Selective synthesis of conformationally restricted mono-cyclopentadienyl titanium(iv) complexes of p-tBu-calix[6]arene

“…1 Their conformational flexibility results in a variety of metal binding environments, and allows several metal centres to be accommodated simultaneously. Calix [4]arenes usually adopt the cone conformation when forming metal complexes, using a preorganised set of four pendant oxygen atoms for chelation. This generally forms molecular assemblies wherein the metal centres bridge two calix [4]arene molecules via phenolate complexation.…”

“…Calix [4]arenes usually adopt the cone conformation when forming metal complexes, using a preorganised set of four pendant oxygen atoms for chelation. This generally forms molecular assemblies wherein the metal centres bridge two calix [4]arene molecules via phenolate complexation. 1 In contrast, the larger ring size and greater flexibility of calix [6]arene presents a more challenging and complex ligand system.…”

“…The facile isolation of 1 and 2 is aided by their precipitation from methanol. Interestingly, similar attempts to prepare calix [4]arene-TiCp complexes from methanol were unsuccessful. For p-t Bu-calix [4]arene cleavage of both cyclopentadienyl ligands occurs for a range of metal: calix [4]arene ratios.…”

“…Interestingly, similar attempts to prepare calix [4]arene-TiCp complexes from methanol were unsuccessful. For p-t Bu-calix [4]arene cleavage of both cyclopentadienyl ligands occurs for a range of metal: calix [4]arene ratios. Success in preparing the monocyclopentadienyl titanium complexes of calix [6]arene possibly arises from the rapid formation and precipitation of the TiCp-calix [6]arene complexes from methanol, which protects the remaining Cp group from cleavage.…”

“…Success in preparing the monocyclopentadienyl titanium complexes of calix [6]arene possibly arises from the rapid formation and precipitation of the TiCp-calix [6]arene complexes from methanol, which protects the remaining Cp group from cleavage. Another aspect of the calix [6]arene, but not calix [4]arene, is possible kinetic protection of the first-formed monocyclopentadienyl complex by its binding in the cavity of the now inverted double cone conformation (see below). t Bu-L[OH] 6 itself crystallises in a double cone conformation 3 rather than the inverted double cone found in 1 and 2.…”