An Adventure in Space (Group) and (Reaction) Time: Divergent Synthesis of Heterobimetallic Complexes of Zinc with Lewis Acids

Abstract

Assembly of heterobimetallic complexes is challenging due to the propensity of ditopic ligands to bind metals unselectively. This challenge is exacerbated in situations in which two redox-inactive metals are to be coordinated within one ligand framework, as such metals can bind in a variety of coordination environments. In this thesis, the preparation and isolation of four heterobimetallic complexes of zinc, a redox-inactive first-row transition metal, with a range of other redox-inactive Lewis acidic metals (Na+, Ca2+, Nd3+, and Y3+) are reported. The complexes were prepared via a divergent route in which a common monometallic zinc complex featuring a crown-ether-like site within a macrocyclic structure was selectively metallated with triflate salts of sodium, calcium, neodymium, and yttrium. One-dimensional 1H and two-dimensional 1H–1H Correlation Spectroscopy (COSY) Nuclear Magnetic Resonance (NMR) studies provide robust support for synthesis of the target heterobimetallic compounds. Single crystals suitable for X-ray diffraction analysis were grown of the [Zn,Nd] complex, revealing the expected atomic connectivity within the macrocyclic framework. In the solid state, the zinc center is five-coordinate, with a terminal acetonitrile ligand; this finding contrasts with the structure of the analogous [Ni,Nd] complex that instead features a four-coordinate nickel center. These results are discussed in the context of developing model compounds for study of the spectroscopic and electrochemical properties of heterobimetallic complexes containing redox-inactive Lewis acids.