Mechanistic study of metalation of 5, 10, 15, 20-tetraphenylporphyrin in acetonitrile

Nakano, Yuko; Sugimoto, Yumi; Inada, Yuji; Funahashi, Shigenobu

doi:10.1016/s0162-0134(97)80004-9

Cited by 2 publications

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“…Rate-Determining Step for Cu(II) Ion Incorporation into Porphyrin in scCO 2 . According to the recent investigations on the metalation reaction of porphyrins, − it has been pointed out that the nucleophilic attack of the first pyrrolenine nitrogen on the solvated metal ion is the rate-determining step for the overall metal ion incorporation reaction. Therefore, the nucleophilic attack of the pyrrolenine nitrogen of H 2 tpfpp is expected to be included in the rate-determining step.…”

Section: Resultsmentioning

confidence: 99%

Kinetics and Mechanism for the Metalation of 5,10,15,20-Tetrakis(pentafluorophenyl)porphyrin with Bis(β-diketonato)copper(II) Complexes in Supercritical Carbon Dioxide and n-Hexane

et al. 2003

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The copper(II) ion incorporation reactions into 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin (H2tpfpp) to form the Cu(tpfpp) complex have been kinetically investigated with bis(β-diketonato)copper(II) complexes (CuL2) such as bis(1,1,1,5,5,5-hexafluoropentane-2,4-dionato)copper(II) (Cu(hfac)2), bis(1,1,1-trifluoropentane-2,4-dionato)copper(II) (Cu(tfac)2), bis(2,2,6,6-tetramethylheptane-3,5-dionato)copper(II) (Cu(hmac)2), and bis(pentane-2,4-dionato)copper(II) (Cu(acac)2) in supercritical carbon dioxide (scCO2) using a previously developed stopped-flow instrument and spectrophotometric cell. Saturation dependence was observed for the conditional first-order rate constants (k obs) as a function of the mole fraction of excess CuL2 (x Cu): k obs = k 2 K 1 x Cu/(1 + K 1 x Cu), where K 1 is the preequilibrium constant for the fast outer sphere association between H2tpfpp and CuL2 and k 2 is the first-order rate constant for the rate-determining copper(II) ion incorporation into the porphyrin core. Under constant temperature (333 K) and pressure (20.0 MPa), the K 1 values are in the order of Cu(hfac)2 < Cu(tfac)2 < Cu(hmac)2 < Cu(acac)2; this trend has been interpreted by the differences in the solvation energy of the CuL2 complexes in scCO2 and in the electrostatic repulsion between H2tpfpp and CuL2 anticipated in the outer sphere association complex. On the other hand, the k 2 values are in the following order: Cu(hfac)2 > Cu(tfac)2 > Cu(hmac)2 > Cu(acac)2. This order may be explained by the affinity of CuL2 for the nucleophile of the pyrrolenine nitrogen, the easiness of dissociation of the β-diketonate ligand, and the electrostatic repulsion between H2tpfpp and CuL2. The thermodynamic and kinetic parameters in scCO2 were obtained as follows: K 1 = (5.2 ± 0.1) × 104 (333 K, 20.0 MPa), ΔH 1 ° = 76 ± 2 kJ mol-1 (20.0 MPa), ΔS 1 ° = (3.2 ± 0.7) × 102 J mol-1 K-1 (20.0 MPa), ΔV 1 ° = (7.9 ± 0.6) × 102 cm3 mol-1 (333 K), k 2 = (2.7 ± 0.3) × 10-4 s-1 (333 K, 20.0 MPa), Δ‡ H 2 ° = −49 ± 9 kJ mol-1 (20.0 MPa), Δ‡ S 2 ° = (−4.6 ± 0.3) × 102 J mol-1 K-1 (20.0 MPa), and Δ‡ V 2 ° = (−4.4 ± 0.6) × 102 cm3 mol-1 (333 K). In addition, the reaction of H2tpfpp with Cu(hfac)2 has been studied in n-hexane in order to compare the results in scCO2 with those in a conventional nonpolar solvent.

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