Structure and properties of a nonheme pentacoordinate iron(II) complex with a macrocyclic triazapyridinophane ligand

A macrocyclic ligand, N,N′,N″-tribenzyl-2,11,20-triaza[3,3,3] (2,6)pyridinophane (BAPP), was used to prepare an iron(II) complex as a nonheme model complex, [(BAPP)Fe]⁺² (1). X-ray crystallography of a colorless crystal of 1 revealed that BAPP acted as a pentadentate ligand due to geometrical strain for the formation of a six-coordinate iron(II) complex by BAPP. As a result, the iron center revealed a significantly distorted square pyramidal geometry similar to that found in the active site of taurine dioxygenase (tauD). In the reaction of 1 with PhIO, no intermediate was observed in the UV-visible region of spectrometer at low temperatures. Catalytic oxidations of triphenyl phosphine with PhIO at -40°C revealed that 1 was able to convert triphenyl phosphine to triphenyl phosphine oxide. Thioanisole was also oxidized to the corresponding methylphenyl sulfoxide under the same conditions.