Assembly and disassembly of a metastable bis-phosphine-based copper(I) helicate.

The synthesis of chelate complexes from bidentate ligands that are formed by self-assembly of simpler monodentate fragments has recently been developed as a new concept with considerable potential for application in catalysis studies. Ligand assembly can be accomplished through direct pairing of fragments with complementary binding motifs, or by fixing two ligand fragments to a suitable template. The individual components normally join through noncovalent interactions such as hydrogen bonding, formation of coordinative bonds, or electrostatic attraction (e.g. anion sequestering), which allow rapid assembly and disassembly of the aggregates and the correction of improper connections. On the other hand, the same type of self-assembly processes was also successfully employed to generate supramolecular architectures such as molecular polygons and three-dimensional cages or polyhedra, and even chiral helicates. Controlled formation of these supramolecular architectures is normally accomplished either by mixing of preformed ligand strands with suitable metal ions or by hierarchical assembly of simple coordination compounds with additional binding sites or reactive units, which is triggered by, for example, displacement of a labile ligand, a redox reaction, or addition of suitable spacers. In both methodologies, constituents and final product are in equilibrium, and the supramolecular architecture is considered to form the most stable aggregate under the chosen reaction conditions. We showed previously that catechol phosphine 1 assembles with various Lewis acids to give template-based bidentate phosphine ligands that readily formed metal complexes. In particular, reaction with borates gave an anionic bidentate phosphine [HNEt3]2, which was easily converted into a chelate complex 3 a upon treatment with silver triflate (Scheme 1). In extending this chemistry to the other uni-