Macrocyclic Binucleating β-Diketiminate Ligands and Their Lithium, Aluminum, and Zinc Complexes

The incorporation of rigid aromatic linkers into β-diketiminate ligands creates a binucleating scaffold that holds two metals near each other. This paper discloses the synthesis, characterization, and reactivity of mBin2-, which has a meta-substituted xylylene spacer, and pBin2-, which has a para-substituted xylylene spacer. Lithium, aluminum, and zinc complexes of each ligand have been isolated, and in some cases characterized by X-ray crystallography. The lithium complexes are coordinated to solvent-derived THF ligands, while the zinc and aluminum complexes have alkyl ligands. Complexes of the mBin2- ligand have an anti conformation in which the metals are on opposite sides of the macrocycle, while pBin2- complexes prefer a syn conformation. The 1H NMR spectra of the complexes demonstrate that the conformations interconvert rapidly in the lithium complexes and less rapidly in the zinc and aluminum complexes.