Formation of Stable NiIII N-Confused Porphyrins Aided by a 3-Ethoxy Group

We report the synthesis, characterization, and reactivities of two stable Ni-III N-confused porphyrin (NCP) complexes. Metalation of 3-OEt NCP 1 with NiCl2 . 6H(2)O in CHCl3/EtOH gave 3-OEt Ni-II NCP 3 initially, which was easily oxidized in air to form the Ni-III complex of NCP inner C-oxide 4. Bis-ethoxy-modified Ni-III complex 5 was synthesized by oxidation of 3 with PIFA in ethanol and CHCl3. The structures of 4 and 5 were determined by single-crystal X-ray diffraction analysis. An unusually long Ni-III-C bond (2.170(9) angstrom) was observed in 4. The g-factor (g>2.1) observed in the EPR spectra of 4 and 5 further confirmed that they are paramagnetic Ni-III complexes. Comparative experiments showed that the 3-ethoxy group plays an important role in the formation of 4 and 5. Reduction of 4 and 5 with NaBH4 regenerated complex 3.

Automated summary

This study reported the synthesis, characterization, and reactivities of two stable Ni-III N-confused porphyrin (NCP) complexes. The role of the 3-ethoxy group in the formation of Ni-III NCP complexes was highlighted in comparative experiments. The structures of the complexes were determined by single-crystal X-ray diffraction analysis, and the paramagnetic nature of the Ni-III complexes was confirmed by EPR spectra.