Synthesis, structure and properties of a five-coordinate oxophosphorus(V) meso-triphenylcorrole

Treatment of six-coordinate (5,10,15-triphenylcorrole) dihydroxyphosphorus(V) [P(TPC)(OH)₂] with trifluoroacetic acid (TFA) in CH₂Cl₂ for 30 min at room temperature followed by recrystallization gave stable five-coordinate (5,10,15-triphenylcorrole) oxophosphorus(V) [P(TPC)O] in quantitative yield. The formation of [P(TPC)O] from [P(TPC)(OH)₂] in the presence of TFA was also monitored by NMR, absorption and fluorescence spectroscopic titration studies. The structure of the isolated [P(TPC)O] was confirmed by X-ray crystallography. In [P(TPC)O], the corrole ring is distorted, and the P^V ion is displaced by 0.456 Å from the N₄ plane towards the axial oxygen atom. This is unlike six-coordinate (5,10,15-triphenylcorrole)dimethoxyphosphorus(V) [P(TPC)(OCH₃)₂], in which the P^V ion lies in the porphyrin plane. NMR, absorption and fluorescence spectroscopy and electrochemical studies indicate that [P(TPC)O] exhibits interesting and distinct properties, which differ from the six-coordinate [P(TPC)(OCH ₃)₂]. Attempts to reduce the P^V complex [P(TPC)O] to its corresponding P^III complex by treating it with LiAlH₄ resulted in the formation of six-coordinate (5,10,15-triphenylcorrole)dihydridophosphorus(V) [P(TPC)H₂].