Intramolecular benzoate exchange in benzoato meso-tetra (4-methoxyphenylporphyrinato) thallium(III), Tl(tmpp)(C6H5CO2)

Article abstract of DOI:10.1016/S0277-5387(96)00479-2

The new compound benzoato meso-tetra(4-methoxyphenylporphyrinato)thallium(III), Tl (tmpp) (C₆H₅CO₂), has been synthesized and its molecular structure determined by X-ray analysis. The coordination sphere of the Tl³⁺ ion is an approximate square-based pyramid in which the apical site is occupied by an asymmetric-bidentate C₆H₅CO^-₂ group. The average Tl - N bond distance is 2.24(1) A and the Tl atom is displaced 0.811 A from the porphyrin plane. The Tl(1) - O(5) and Tl(1) - O(6) distances are 2.57(2) and 2.27(2) A, respectively. Variable temperature ¹³C NMR measurements show that the benzoato group of Tl (tmpp) (C₆H₅CO₂) in CD₂Cl₂ solvent undergoes intramolecular exchange. In the slow exchange region, the carbonyl and C_1'' carbons of the benzoato group are separately located at 167.8 ppm [with ²J(Tl-¹³C) coupling constant 212 Hz] and 128.3 ppm [with ³J (Tl-¹³C) coupling constant 282 Hz] for Tl(tmpp)(C₆H₅CO₂) in CD₂Cl₂ at - 90°C. In the fast exchange region, the C*OO and C_1'' carbons of the C₆H₅CO^-₂ ligand in CD₂Cl₂ at 21°C are singlets at 168,4 and 130.3 ppm, respectively. The comparison of the ring current effect (Δδ) for the benzoate ligand of Tl(tmpp)(C₆H₅CO₂) and benzoato meso-tetra(4-methoxyphenylporphyrinto)tin(IV), Sn(tmpp)(C₆H₅CO₂)₂, is also reported.