Abstract
In this study, a methyl group on the classic tetramethylcyclam (TMC) ligand framework is replaced with a benzylic group to form the metastable [Fe(IV) (O(syn) )(Bn3MC)](2+) (2-syn; Bn3MC=1-benzyl-4,8,11-trimethyl-1,4,8,11-tetraazacyclotetradecane) species at -40 °C. The decay of 2-syn with time at 25 °C allows the unprecedented monitoring of the steps involved in the intramolecular hydroxylation of the ligand phenyl ring to form the major Fe(III) -OAr product 3. At the same time, the Fe(II) (Bn3MC)(2+) (1) precursor to 2-syn is re-generated in a 1:2 molar ratio relative to 3, accounting for the first time for all the electrons involved and all the Fe species derived from 2-syn as shown in the following balanced equation: 3 [Fe(IV) (O)(L(Ph) )](2+) (2-syn)→2 [Fe(III) (L(OAr) )](2+) (3)+[Fe(II) (L(Ph) )](2+) (1)+H(2) O. This system thus serves as a paradigm for aryl hydroxylation by Fe(IV) =O oxidants described thus far. It is also observed that 2-syn can be intercepted by certain hydrocarbon substrates, thereby providing a means to assess the relative energetics of aliphatic and aromatic C-H hydroxylation in this system.