Syntheses and Properties of Metalated Tetradehydrocorrins.

The monoanionic tetrapyrrolic macrocycle B , C -tetradehydrocorrin (TDC) resides chemically between corroles and corrins. This chemical space remains largely unexplored due to a lack of reliable synthetic strategies. We now report the preparation and characterization of Co(II)- and Ni(II)-metalated TDC derivatives ( [Co-TDC] + and [Ni-TDC] + , respectively) with a combination of crystallographic, electrochemical, computational, and spectroscopic techniques. [Ni-TDC] + was found to undergo primarily ligand-centered electrochemical reduction, leading to hydrogenation of the macrocycle under cathodic electrolysis in the presence of acid. Transient absorption (TA) spectroscopy reveals that [Ni-TDC] + and the two-electron-reduced [Ni-TDC] - possess long-lived excited states, whereas the excited state of singly reduced [Ni-TDC] exhibits picosecond dynamics. The Co(I) compound [Co-TDC] is air stable, highlighting the notable property of the TDC ligand to stabilize low-valent metal centers in contradistinction to other tetrapyrroles such as corroles, which typically stabilize metals in higher oxidation states.