The use of bisoxazoline ligands in the preparation of selective, self -assembled supramolecular structures

Interest in self-assembled organometallic supramolecular structures has increased considerably over the last few years, due to the relative ease of constructing large molecules by this approach as compared to traditional methods of organic synthesis. One challenge of self-assembly is controlling which individual ligand units will assemble onto the metal during the formation of the complex. We have found that the use of bisoxazoline ligands will allow for the control of the ligand order, as well as the overall complex architecture, and we propose that this approach may have applications toward the rational construction of novel supramolecular structures. When an enantiomeric mixture of bisoxazoline ligands is added to zinc(II) triflate, the ligands self-assemble exclusively into heterochiral complexes, rather than the alternative homochiral complexes. The chiral nature of the ligand dictates the assembly of the complex, in which coordination of the same enantiomer to the metal is disfavored. Through modification of the bisoxazoline ligand before the assembly of the complex, large, multinuclear species can be designed which consist of mixed ligands that will assemble into complexes in a practical, predictable manner. Within this work, rational methods for the construction of novel supramolecular structures via the enantioselective self-assembly of ligand-metal complexes have been developed. A number of novel, chiral bisoxazoline and tetraoxazoline ligands have been constructed, including a previously unknown class of protic bisoxazoline ligands. These protic bisoxazolines are capable of forming non-centrosymmetric neutral complexes upon complexation to zinc and treatment with mild base. These complexes show increased stability to the presence of solvents and other ligands, while retaining the self-assembly concept to control the order of ligand binding. Through rational ligand design we can manipulate the electron withdrawing or donating properties of these ligands, resulting in complexes that may have the potential to act as nanostructured acceptor-donor complexes