Kinetic effect of cosolvents on the metalation reaction of porphyrin with bis(β-diketonato)copper(II) in supercritical carbon dioxide

The kinetic effect of cosolvents on the Cu(II) ion incorporation into 5,10,15,20-tetrakis-(pentafluorophenyl)porphyrin (H2tpfpp) with bis(1,1,1,5,5,5-hexafluoropentane-2,4-dionato)copper(II) (Cu(hfac)2) in supercritical carbon dioxide has been investigated using methanol, ethanol, and 1-propanol as the cosolvent. The conditional first-order rate constants showed a saturation dependence versus the mole fraction of a large excess Cu(hfac)2. The metalation reaction is postulated to consist of a fast pre-equilibrium of the outer-sphere association between Cu(hfac)2 and H2tpfpp and a rate-determining Cu(II) ion incorporation into the porphyrin core. The apparent reaction rates are accelerated by the addition of cosolvents and the effects will be discussed in relation to the solvation of the cosolvents.