Synthesis and Characterization of an Air‐Stable Tin(IV) β‐Tetracyanoisophlorin Complex: Enhanced Antiaromaticity through Metal Complexation

Isophlorins, which are two‐electron reduced porphyrins, have garnered significant interest because of their potential antiaromaticity and unique electronic properties. However, the isolation of stable antiaromatic isophlorins remains challenging because they are prone to oxidation or reduction to the corresponding aromatic molecules, or are structurally distorted, resulting in loss of antiaromaticity. Here, we report the synthesis and characterization of a Sn(IV) β‐tetracyanoisophlorin complex obtained through two‐electron reduction of the corresponding Sn(IV) β‐tetracyanoporphyrin complex. This Sn(IV) complex exhibits enhanced antiaromaticity owing to its highly planar structure, facilitated by the central Sn atom. X‐ray crystal diffraction analysis revealed that the Sn(IV) isophlorin complex contains two methoxy groups as axial ligands and that it exists as a divalent anion, demonstrating the oxophilic nature of the Sn(IV) isophlorin complexes. Notably, this Sn(IV) isophlorin complex is stable under air, distinguishing it from previously reported Si(IV) and Ge(IV) isophlorin complexes without cyano groups. This study thus presents the first isolation of an air‐stable metal complex of antiaromatic isophlorin, opening new possibilities for exploring the unique properties of antiaromatic porphyrinoids for various applications, including catalysis and materials science.