MOLECULAR-STRUCTURE OF ACETATO O-TETRA(4-METHOXYPHENYLPORPHYRINATO)THALLIUM(III), TL(TMPP)(OAC), AND C-13 NMR INVESTIGATION OF ITS HOMOLOG CYANO O-TETRA(4-METHOXYPHENYLPORPHYRINATO)THALLIUM(III), TL(TMPP)(CN)

The new compound acetato o-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 fr om the porphyrin mean plane was 0.808 Angstrom. The geometry around th e 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)Angstrom. An asymmet ric-bidentate acetato group is coordinated to the thallium(III) atom. The free energy of activation Delta G(224) for the acetato group of T l(tmpp)(OAc) in CD2Cl2 solvent undergoing intramolecular exchange has been derived to be 48.4 kJ mol(-1) through H-1 NMR temperature-depende nt measurements. In the intermediate exchange region, neither the carb onyl nor methyl signals of the acetate ligand for Tl(tmpp)(OAc) in CD2 Cl2, solvent in C-13 NMR spectra was found at 20 degrees C. In the slo w exchange region, the methyl and carbonyl carbons of the acetato grou p are separately located at 17.7 ppm [with (3)J(Tl-C-13) coupling cons tant 275 Hz] and 173.9 ppm [with (2)J(Tl-C-13) coupling constant 230 H z], respectively, for the Tl(tmpp)(OAc) in CD2Cl2 at -90 degrees C. Th e C-13 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 degrees C) [with (1)J(Tl-205-C-13) coupl ing constant 5287.3 Hz and (1)J(Tl-203-C-13) 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). Copyright (C) 1996 Elsevie r Science Ltd