Zq. Tian et al., FORMATION OF BOTH PRIMARY AND SECONDARY N-ALKYLHEMINS DURING HEMIN-CATALYZED EPOXIDATION OF TERMINAL ALKENES, Journal of the American Chemical Society, 117(1), 1995, pp. 21-29
The N-alkylhemin formation during iron(III) porphyrin-catalyzed epoxid
ation of alkenes is studied in a homogeneous system using pentafluoroi
odosobenzene (PFIB) as the oxidant. The system is a model for the enzy
me cytochrome P-450. A second N-alkyl species other than the well-docu
mented primary N-alkylhemin is observed during the oxidation of termin
al alkenes. It is unstable and decomposes under the reaction condition
s. It is also a catalyst for alkene epoxidation by PFIB. Its character
istics are consistent with a secondary N-alkylhemin. The kinetics were
partially resolved, and rate constants-were estimated for the formati
on of both N-alkylhemins, for the decomposition of the secondary N-alk
ylhemin, and for the epoxidation by the hemin and the N-alkylhemins. T
he partition ratios were measured by a kinetic method, which provides
better insight for the mechanisms of both N-alkylation and epoxidation
than the measurements by product analysis using heterogeneous systems
. We suggest that alkenes reversibly inhibit cytochrome P-450 through
the formation of the unstable N-alkylporphyrin species.