Synthesis and electrochemistry of tetraphenylporphyrins containing an antimony-carbon sigma-bond

The following five antimony(V) tetraphenylporphyrins with sigma-bonded antimony-carbon bonds were synthesized: [(TPP)Sb(CH3)(2)](PF6-)-P-+, [(TPP)Sb(OCH3)(OH)](PF6-)-P-+, [(TPP)Sb(CH3)(OH)](ClO4-)-Cl-+, [(TPP)Sb(CH3)-(OCH3)](ClO4-)-Cl-+, and [(TPP)Sb(CH3)(F)](PF6-)-P-+. Each compound is stable toward air and moisture and has a high melting point (>250 degrees C). The electrochemistry and spectroelectrochemistry of these sigma-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 sigma-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 pi 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-)-P-+ is also presented: monoclinic, space group C2/c, Z = 8, a = 24.068(5) Angstrom, b = 19.456(4) Angstrom, c = 18.745(3) Angstrom, beta = 94.69(2)degrees, R = 0.056.