Synthesis and Electrochemistry of Tetraphenylporphyrins Containing an Antimony−Carbon σ-Bond

The following five antimony(V) tetraphenylporphyrins with σ-bonded antimony−carbon bonds were synthesized:  [(TPP)Sb(CH₃)₂]⁺PF₆^-, [(TPP)Sb(OCH₃)(OH)]⁺PF₆^-, [(TPP)Sb(CH₃)(OH)]⁺ClO₄^-, [(TPP)Sb(CH₃)(OCH₃)]⁺ClO₄^-, and [(TPP)Sb(CH₃)(F)]⁺PF₆^-. Each compound is stable toward air and moisture and has a high melting point (>250 °C). The electrochemistry and spectroelectrochemistry of these σ-bonded porphyrins were examined in benzonitrile or dichloromethane containing 0.1 M tetrabutylammonium perchlorate as supporting electrolyte and the data compared to those for three previously synthesized OEP derivatives containing similar σ-bonded and/or anionic axial ligands. Each porphyrin shows two reversible reductions and up to a maximun of one oxidation within the potential window of the solvent. Spectroelectrochemical data indicate formation of a porphyrin π anion radical upon the first reduction as do ESR spectra of the singly reduced species. However, a small amount of the Sb(III) porphyrin products may be generated via a chemical reaction following electron tranfer. An X-ray crystallographic analysis of [(TPP)Sb(CH₃)(F)]⁺PF₆^- is also presented:  monoclinic, space group C2/c, Z = 8, a = 24.068(5) Å, b = 19.456(4) Å, c = 18.745(3) Å, β = 94.69(2)°, R = 0.056.