Gas-phase rates of heme-model olefin epoxidation

FT-ICR and DFT show iron(IV)–oxo porphyrin cation radicals epoxidize olefins with rates that track substrate ionization energy.

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How do experimental epoxidation rates trend with olefin electronic structure?

They correlate linearly with substrate ionization potential; electron transfer to the oxidant is rate determining.

What KIE was measured for cyclohexene vs cyclohexene-d10?

kH/kD very close to 1, so H-atom abstraction is not rate determining.

What efficiency range is reported for terminal olefins?

About 0.001% to 0.08% of the collision rate, versus up to ~50% for electron-rich monoterpenes.

What upper bound is placed on the oxidant’s electron affinity?

EA of gaseous [FeIV(O)(TPFPP+·)]+ must be lower than 8.2 eV.

How was the TPFPP Compound I analogue generated?

Iodosylbenzene (0.5 mM) plus [FeIII(TPFPP)]Cl (10 μM) in 1:1 MeOH/CH2Cl2 at −40 °C.

How large is the estimated error on absolute kexp?

About ±30% (reproducibility within 10%).

What extra channel is seen with cyclohexene?

About 25% molecular addition to give an ion matching [Fe(TPFPP)(c-C6H10)O]+.

Is gas-phase hydroxylation competitive with epoxidation?

The work highlights regioselective epoxidation over hydroxylation in the gas phase.

How stable is the naked five-coordinate ion to unimolecular decay?

kdiss ≤ 0.001 s−1.

What DFT electron affinity is quoted for an SH− axial ligand model?

3.06 eV for X = SH− (vs 6.41 and 6.12 eV for imidazole or tyrosinate).

Which olefins were in the computational/experimental panel?

Ethene through 2-pinene, including cyclohexene, styrene, and 2-butene isomers.