Session: ACS Award for Encouraging Women into Careers in the Chemical Sciences: Symposium Honoring Katherine Franz :

The tethering of metal complexes is a facile method to produce coordination complexes with multiple metal sites, which can be referred to as molecular tweezers. Due to their prevalence in nature and strong binding to metals as N₄^2- macrocycles, porphyrins have been reported in several tethered complexes. Dibenzotetramethyl-tetraaza[14]annulene (tmtaa) exhibits the same N₄^2- sites for binding as porphyrins, but syntheses of tethered tmtaa and its metallated derivatives have yet to be reported despite their simple and inexpensive one-pot preparations. In contrast to aromatic, 18-π-electron porphyrins, tetraaza[14]annulenes are antiaromatic and contain 16-π-electrons, which diversifies the design and application of tethered macrocycles. This presentation reports the synthesis and characterization of tethered tmtaa both as a free ligand and a nickel complex.

The tethered product was prepared via the selective reaction of 2,6-isophthaloyl chloride at the methine positions of two tmtaa molecules (1). A 1:2 ratio of 2,6-isophthaloyl chloride to (1) under reflux conditions produced the single tethered product (SIT-tmtaa) (2), along with a small quantity of the double tethered product (DIT-tmtaa) (3). By changing the ratios of these two reagents to 2:2 (Fig. 1), (3) was observed in a crude mixture using ¹H NMR and ESI-MS, but was unable to be purified for further characterization. (2) was successfully recrystallized from acetonitrile and characterized with ESI-MS, UV-vis, ¹H and ¹³C NMR, and X-ray crystallography. DFT computations were also performed to ascertain the geometry of (1), (2), and (3).

The di-nickel(II) complex of (2) was produced using nickel (II) acetate and was characterized by ESI-MS, ¹H and ¹³C NMR, and UV-vis. DFT was also utilized to predict the optimal geometry of the molecule. The sucessful synthesis of the free ligand and the nickelated complex offer promise for further research into tethered antiaromatic ligands and their potential applications.

<b>Figure 1 (From paper): Synthesis of (2) and (3)</b>

Figure 1 (From paper): Synthesis of (2) and (3)

Bradford Wayland

Appearances