Aminotroponiminates: Alkali Metal Compounds Reveal Unprecedented Coordination Modes

The coordination chemistry of alkalimetal aminotroponiminates (ATIs) was investigated based on (i) a lithium ATI, (ii) the first example of a sodium ATI, and (iii) the first example of a structurally characterized potassium ATI. In the lithium derivative of this series, the ATI ligand adopts a well-known κ2N binding mode. In contrast, the sodium and potassium ATIs show two different types of unprecedented polymeric structures in the solid state, unraveling a surprisingly rich coordination chemistry for the ATI ligand family. In the solid-state structure of the potassium compound, ATI ligands bridge the metal atoms in a μ2-κ2N binding mode. The sodium compound reveals a μ2-κ2Nκ5C coordination mode with an unusual interaction of a metal center with a C7 ATI ligand backbone. NMR studies suggest that this type of interaction might also be accessible in solution. It was further studied by DFT calculations. The tendency of monoanionic ATI ligands to interact with transition-metal centers via their C7 ligand backbone was investigated experimentally and theoretically using Rh+ and W0 as examples for potentially arenophilic metals.