Molecular structure of acetato meso-tetra (4-methoxyphenylporphyrinato)thallium(III), Tl(tmpp)(OAc), and 13C NMR investigation of its homolog cyano meso-tetra (4-methoxyphenylporphyrinato)thallium(III), Tl(tmpp)(CN)

Abstract

Abstract The new compound acetato meso -tetra(4-methoxyphenylporphyrinato)thallium(III), Tl(tmpp)(OAc), has been synthesized and its molecular structure determined by X-ray analysis. The displacement of the thallium atom from the porphyrin mean plane was 0.808A˚. The geometry around the thallium centre of the Tl(tmpp)(OAc) molecule has Tl-O(1) = 2.29(1) and Tl-O(2) = 2.48(1) and average Tl-Np= 2.211(8)A˚. An asymmetric-bidentate acetato group is coordinated to the thallium(III) atom. The free energy of activation ΔG 224 * for the acetato group of Tl(tmpp)(OAc) in CD 2 Cl 2 solvent undergoing intramolecular exchange has been derived to be 48.4 kJ mol −1 through 1 H NMR temperature-dependent measurements. In the intermediate exchange region, neither the carbonyl nor methyl signals of the acetate ligand for Tl(tmpp)(OAc) in CD 2 Cl 2 solvent in 13 C NMR spectra was found at 20°C. In the slow exchange region, the methyl and carbonyl carbons of the acetato group are separately located at 17.7 ppm [with 3 J (Tl- 13 C) coupling constant 275 Hz] and 173.9 ppm [with 2 J (Tl- 13 C) coupling constant 230 Hz], respectively, for the Tl(tmpp)(OAc) in CD 2 Cl 2 at −90°C. The 13 C resonance of the axial cyano ligand in the title compound cyano meso -tetra(4-methoxyphenylporphyrinato)thallium(III), Tl(tmpp)(CN), was observed at 139.9 ppm (20°C) [with 1 J ( 205 Tl- 13 C) coupling constant 5287.3 Hz and 1 J ( 203 Tl- 13 C) coupling constant 5238.0 Hz]. This indicates that the cyano group is, as cyanide type, axially coordinated to the Tl atom in Tl(tmpp)(CN).