Switchable Aromaticity in an Isostructural Mn Phthalocyanine Series Isolated in Five Separate Redox States

The synthesis and characterization
of a new phthalocyanine (Pc)
Mn-nitride complex, (OEtPc)­MnN (2; OEtPc = 1,4,8,11,15,18,22,25-octaethoxy-Pc), as well as its stable,
readily accessible oxidized (2+ and 22+) and reduced (2–, 22–) congeners is reported. This unique isostructural
series displays switchable aromatic character spanning the aromatic
(2), nonaromatic (22+), and antiaromatic (22–) triad, in addition to the open-shell radical states (2+, 2–). All complexes were structurally characterized and displayed
significant structural distortions at the redox extrema (22+, 22–) consistent with proposed [16 or 18]­annulene π ring
circuit models. Spectroscopic and computational studies further support
these models. This isolated, fully characterized, isostructural series
spanning five redox states (22+, 2+, 2, 2–, 22–) is unique in both the Pc and related macrocyclic
(ex. porphyrinoids) literature and may offer direct insight into structural–electronic
correlations driven by switchable aromaticity.