Hierarchical lithium-templated assembly of helicate-type complexes:: How versatile is this reaction?

Catechol ligands that bear carbonyl functions such as esters or aldehydes in the 3-position (1a-c-H-2) form triple-stranded, helicate-type complexes [Li-3(1a-c)(6)Ti-2](1) with titanium(IV) and the corresponding double-stranded compounds [Li-2(1a-c)(4)B-2] with boron(III) in hierarchical, lithium-templated processes. The related 8-hydroxyquinoline ligands 2a,bH can be used for the formation of similar complexes [Li-3(2a,b)(6)M-2](+) with cobalt(II), nickel(II), or zinc(II). A prerequisite for the formation of the lithium-bridged dimers is a negative charge of the mononuclear complexes, which are able to electrostatically attract the lithium cations and thus compensate the repulsion between the cations. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)