Molecular structure of [Tl(tpp)(O2CCF3)] and 19F dynamic nuclear magnetic resonance of it and [Tl(tmpp)(O2CCF3)][tpp = 5,10,15,20-tetraphenylporphyrinate, tmpp = 5,10,15,20-tetra(4-methoxyphenyl)porphyrinate]

Abstract

The crystal structure of (meso-5,10,15,20-tetraphenylporphyrinato)(trifluoroacetato)thallium(III), [Tl(tpp)(O₂CCF₃)], was determined. The co-ordination sphere of the Tl³⁺ ion is an approximate square-based pyramid in which the apical site is occupied by an asymmetric bidentate O₂CCF₃^– group. The average Tl–N bond distance is 2.200(5)Å and the Tl atom is displaced 0.741 Å from the porphyrin plane. The Tl–O(1) and Tl–O(2) distances are 2.309(7) and 2.64(1)Å, respectively. The extent of dissociation of [5,10,15,20-tetra(4-methoxyphenyl)porphyrinato](trifluoroacetato)thallium(III), [Tl(tmpp)(O₂CCF₃)], in CD₂Cl₂ was ≈4%. The free energy of activation at the coalescence temperature T_c was for the intermolecular trifluoroacetate exchange between ≈96 of [Tl(tmpp)(O₂CCF₃)] and ≈4% of CF₃CO₂H in CD₂Cl₂ solvent has been found to be ΔG₂₃₈^‡ 45.8 kJ mol^–1 through ¹⁹F NMR temperature-dependent measurements. However, [Tl(tmpp)(O₂CCF₃)] and its homologue [Tl(tpp)(O₂CCF₃)] do not dissociate in [²H₈]tetrahydrofuran. They undergo intramolecular CF₃CO₂^– exchange in this solvent and ΔG₂₁₂^‡(or ΔG₂₀₃^‡) for this process was found to be 44.4 (or 42.0 kJ mol^–1) for [Tl(tpp)(O₂CCF₃)]{or [Tl(tmpp)(O₂CCF₃)]} from ¹⁹F dynamic NMR spectroscopy. In the slow-exchange region the CF₃ and carbonyl (CO) carbons of the CF₃CO₂^– group in [Tl(tpp)(O₂CCF₃)] are separately located at δ 115.9 [¹J(C–F)= 291, ³J(Tl–¹³C)= 239] and 156.5 [²J(C–F)= 37, ²J(Tl–¹³C)= 128 Hz] at – 100 °C.