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 metalation

Abstract

The zinc(II) ion incorporation reaction into 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin (H 2tpfpp) 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) 2L 2]; L=H 2O, CH 3OH) in supercritical carbon dioxide (scCO 2) 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 {H 2tpfpp + [Zn(hfac) 2(CH 3OH) 2]} at 20.5 MPa, and k=7.7 mol −1 dm 3 s −1 at 308.2 K and 20.5 MPa, ΔH ‡=21±1 kJ mol −1, ΔS ‡=−(1.4±0.2)×10 2 J mol −1 K −1 for the reaction system {H 2tpfpp + [Zn(hfac) 2(H 2O) 2]} at 20.5 MPa. The activation volumes (Δ V ‡) at 308.2 K are (4.0 ± 0.4) × 10 2 cm 3 mol −1 for [Zn(hfac) 2(CH 3OH) 2] and (3.8±0.7)×10 2 cm 3 mol −1 for [Zn(hfac) 2(H 2O) 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(CH 3OH) 2] are formed by hydrogen bonding with the formation constants of β 1=(1.2±0.3)×10 2 mol −1 dm 3 and β 2=(1.4±0.3)×10 4 mol −2 dm 6 at 323.3 K and 20.5 MPa, and the outer-sphere adducts, [Zn(hfac) 2(CH 3OH) 2]–(CH 3OH) and [Zn(hfac) 2(CH 3OH) 2]–(CH 3OH) 2, are non-reactive. The mechanistic consideration and specific cosolvent effect will be described on the basis of the rate law and activation parameters.