Synthesis and Characterization of Bis(pyridylimino)isoindolide Alkali Metal Complexes in Three Redox States

Non-innocent ligands (NILs) like bis(pyridylimino)isoindolide (BPI) play crucial roles in coordination chemistry, biosciences, catalysis and material sciences. Investigating the isolated redox states of NILs is inevitable for understanding their redox-activity and fine-tuning the properties of corresponding metal complexes. The limited number of fundamental studies on the coordination behavior and redox chemistry of reduced BPI species is suggested to hamper further applications of the title compounds. This work describes for the first time the isolation of alkali metal complexes of BPI and Me2BPI in three different oxidation states and their characterization by means of NMR or EPR spectroscopy, DFT calculations, and SC-XRD studies. The latter revealed the connection between bond orders in the ligand scaffold and its oxidation state. The paramagnetic compound Me2BPI-K-2 was isolated as a coordination copolymer with 18-crown-6, which enabled the characterization of the dianionic BPI radical. Furthermore, the so-far unknown trianionic state of BPI was reported by the isolation of BPI-K-3. This divulges an unprecedented bis(amidinato)isoindolide coordination mode.