1,4‐Diphosphinines from Imidazole‐2‐thiones

Abstract 1,4‐Diphosphinines that are fused to two thiourea units were synthesized from the corresponding tricyclic 1,4‐dichloro‐1,4‐dihydro‐1,4‐diphosphinines, and their structures and spectroscopic features are described. Electrochemical studies revealed very low oxidation potentials, which are due to the effective π‐interaction between the 1,4‐diphosphinine ring and the orbitals of the two ylidic C=S bonds. In accordance with the low‐lying LUMO, which is largely localized at the two phosphorus centers, dianion formation is strongly preferred. Despite the small HOMO–LUMO gap, which is in accordance with the red color of the title compounds, theoretical calculations suggest considerable aromaticity for the 1,4‐diphosphinine ring.