Salicylate exchange in meso-tetraphenylporphyrinato salicylato thallium(III), Tl(tpp) (2-OH-C6H4CO2) and C-13 NMR investigation of its homolog thiocyanato (meso-tetra-p-tolyl-porphyrinato)thallium(III), Tl(tptp)(SCN)

Abstract

This work determines the crystal structure of meso-tetraphenylporphyrinato salicylato thallium(III), Tl(tpp) (2-OH-C6H4CO2)(or Tl(tpp)(SA)). The coordination sphere of the Tl3+ ion is an approximately square-based pyramid in which a chelating bidentate 2OH-C6H4CO2- group occupies the apical site. The average Tl(1)-N bond distance is 2.221 Angstrom and the Tl atom is displaced 0.76 Angstrom from the porphyrin plane. The Tl(1)-O(1) and Tl(1)-O(2) distance are 2.36(1) and 2.47(1) Angstrom, respectively. Variable temperature C-13 NMR measurements reveal that the salicylato group of Tl(tpp)(SA) in CD2Cl2 solvent undergoes a ligand exchange. In the slow exchange region, the carbonyl and C-1" carbons of the salicylato group are separately located at 169.6 ppm [with a (2)J(Tl-C-13) coupling constant of 157 Hz] and 111.5 ppm [with a (3)J(Tl-C-13) coupling constant of 180 Hz] for Tl(tpp)(SA) in CD2Cl2 at -90 degrees C. In the fast exchange region, the C*O and C-1" carbons of the 2-OH-C6H4CO2- ligand in CD2Cl2 at 24 degrees C are singlets at 169.8 and 112.5 ppm, respectively. The C-13 resonance of the axial isocyanato ligand in the compound thiocyanato (meso-tetra-p-tolyl-porphyrinato)thallium(III), Tl(tptp)(SCN), was observed at 110.7 ppm (24 degrees C) with (2)J(Tl-C-13) coupling constant 253 Hz. This finding suggests that thiocyanato group is, as thiocyanate type, axially coordinated to the Tl atom in Tl(tptp)(SCN). In addition, there is no SCN- exchange in the same compound. (C) 1998 Elsevier Science Ltd. All rights reserved.