Steric Modifications Tune the Regioselectivity of the Alkane Oxidation Catalyzed by Non-Heme Iron Complexes

Iron complexes with the tetradentate N-donor ligand N,N′-di­(phenylmethyl)-N,N′-bis­(2-pyridinylmethyl)-1,2-cyclohexanediamine
(bbpc) are reported. Despite the benzyl groups present on the amines,
the iron compounds catalyze the oxygenation of cyclohexane to an extent
similar to those employing less sterically encumbered ligands. The
catalytic activity is strongly dependent on the counterion, with the
highest activity and the strongest preference for alkane hydroxylation
correlating to the most weakly coordinating anion, SbF6–. The selectivity for the alcohol product over
the ketone is amplified when acetic acid is present as an additive.
When hydrocarbon substrates with both secondary and tertiary carbons
are oxidized by H2O2, the catalyst directs oxidation
toward the secondary carbons to a greater degree than other previously
reported iron-containing homogeneous catalysts.