A Phosphorus(V)-Centered Porphyrin Having Redox- and Air-Stable Axial P-H Bonds

Phosphorus(V)-centered porphyrins (P(V)-porphyrins) are an important class of functional dyes in many fields of research, and axial ligands on the phosphorus atom affect the electronic properties of P(V)-porphyrins and add functions. Herein, we report on the synthesis and characterization of a hitherto unknown P(V)-porphyrin having hydrogen atoms as axial ligands (1⁺·PF₆ ^-, PF₆ ^- is a counter anion). Synthesis of 1⁺·PF₆ ^- was achieved by treatment of dichloro-derivative (2⁺·Cl^-) with LiAlH₄ followed by AgPF₆ via hydride reduction accompanied by one-electron reduction and one-electron oxidation. The porphyrin core of 1⁺·PF₆ ^- is nonplanar but considerably ruffled. The cyclic voltammogram of 1⁺·PF₆ ^- exhibits two reversible waves, which indicates redox couples among 1⁺, neutral radical 1^•, and 1^-. Compound 1⁺·PF₆ ^- is tolerant toward air despite its PH₂ moiety due to the energetically low-lying HOMO (highest occupied molecular orbital) and σ(P-H) orbitals.