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 me

摘要

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( l,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,DELTAH=43.4+-1.4 kJ mol~(-1),DELTAS=-70+-5J mol~(-1) K~(-1) for the reaction system [H_2tpfpp+Zn(htac)_2(CH_3OH)_2]} at 20.5 MPa,and k=7.7 mol~(-1) dm~3s~(-3) at 308.2K and 20.5 MPa,DELTAH =21+-1 kJ mol~(-1),DELTAS=-(1.4+-0.2)X10~2 J mol~(-1) K~(-1) for the reaction system {H_2tpfpp +[Zn(hfac)_2(H_2O)_2]} at 20.5 MPa.The activation volumes (DELTAV) at 308.2 K are (4.0+-0.4)X10~2 cm~3 mol~(-1) for [Zn(hfac)_2 (CH_3OH)_2] and (3.8+-0.7)X10~2cm~3mol~(-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 beta_1=(1.2+-0.3)X10~2 mol~(-1) dm~3 and beta_2=(1.4+-0.3)X10~4 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(htac)_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.