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groups, using iodosobenzene as the oxidant, and saw sensible variations in the relative
rates of epoxidation with structure, indicating that the porphyrins that could bind the
substrates across the face of the metalloporphyrin core were the most effective.
Building on these results, we examined the capability of manganese porphyrin
125
in hydroxylating steroid substrate
129
, again using iodosobenzene as oxidant [191,
192]. Indeed, the reaction was successful, and a single product was produced in which
the C-6 equatorial hydrogen of substrate
129
was replaced with a hydroxyl group in
product
130
. There was even some turnover catalysis, but with only 4 turnovers or so
before the catalyst was oxidatively destroyed.
The turnover problem was solved with porphyrin derivative
131
, in which the fluor-
ines on the phenyl groups greatly stabilized the catalyst against oxidative destruction
[193]. Again with iodosobenzene as the reagent, catalyst
131
converted substrate
129
into its 6-hydroxy derivative
130
, but now with 187 turnovers. We have since produced
catalysts with even higher turnovers for this process [194].
In our catalytic hydroxylations described above we added some pyridine to the solu-
tion to coordinate with one face of the manganese porphyrin, so as to direct an oxygen
atom and the bound substrate to the same face. To avoid this, we synthesized catalyst
