Kinetic study of the metalation reaction of 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin with water and methanol adducts of bis(1,1,1,5,5,5-hexafluoropentane-2,4-dionato)zinc(II) in supercritical carbon dioxide: specific cosolvent effect on the metalat

The zinc(II) ion incorporation reaction into 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin (H2tpfpp) to form the [Zn(tpfpp)] complex has been kinetically investigated using the methanol and water adducts of bis(1,1,1,5,5,5-hexafluoropentane-2,4-dionato)zinc(II) ([Zn(hfac)2L2]; L=H2O, CH3OH) in supercritical carbon dioxide (scCO2) medium at various temperatures and pressures. The metalation reaction is first-order with respect to the porphyrin and Zn(II)–hfac complexes. The kinetic parameters are obtained as follows: k=3.1 mol dm−3 s−1 at 308.2 K and 20.5 MPa, ΔH‡=43.4±1.4 kJ mol−1, ΔS‡=−70±5 J mol−1 K−1 for the reaction system {H2tpfpp + [Zn(hfac)2(CH3OH)2]} at 20.5 MPa, and k=7.7 mol−1 dm3 s−1 at 308.2 K and 20.5 MPa, ΔH‡=21±1 kJ mol−1, ΔS‡=−(1.4±0.2)×102 J mol−1 K−1 for the reaction system {H2tpfpp + [Zn(hfac)2(H2O)2]} at 20.5 MPa. The activation volumes (ΔV‡) at 308.2 K are (4.0 ± 0.4) × 102 cm3 mol−1 for [Zn(hfac)2(CH3OH)2] and (3.8±0.7)×102 cm3 mol−1 for [Zn(hfac)2(H2O)2] in the pressure range from 10 to 35 MPa. In the presence of an excess amount of methanol as a cosolvent, the outer-sphere adducts between methanol and [Zn(hfac)2(CH3OH)2] are formed by hydrogen bonding with the formation constants of β1=(1.2±0.3)×102 mol−1 dm3 and β2=(1.4±0.3)×104 mol−2 dm6 at 323.3 K and 20.5 MPa, and the outer-sphere adducts, [Zn(hfac)2(CH3OH)2]–(CH3OH) and [Zn(hfac)2(CH3OH)2]–(CH3OH)2, are non-reactive. The mechanistic consideration and specific cosolvent effect will be described on the basis of the rate law and activation parameters.