Phosphorus complexes of a triply-fused [24]pentaphyrin

Treatment of an N-fused [24]pentaphyrin with POCl₃ in the presence of triethylamine gave a triply-fused pentaphyrin PO complex through an N-fusion reaction and oxidative C–C bond formation between the pyrrolic β-positions. This complex displays strong antiaromatic character due to its 24π-electronic network as evinced by its ¹H NMR chemical shifts, absorption spectrum, and NICS calculation. The PO complex was reduced with BH₃·SMe₂ to provide P–BH₃ complex with concurrent hydrogenation at the pyrrolic β-positions as a rare case of porphyrinoid P(III) complex.