Oxidation of 5,10,15,20-tetramesitylporphyrinatoiron(III) perchlorate, (TMP)Fe-III(ClO4), with ferric perchlorate in acetonitrile gave a metastable species identified as (TMP)Fe-IV(ClO4)(2) that decayed within seconds to the known isomeric species (TMP center dot+)Fe-III(ClO4)(2). Irradiation of the metastable species with 355 nm laser light gave a highly reactive transient that reacts with simple organic reductants (alkenes and arylalkanes) 5 orders of magnitude faster than known Compound I analogues, (TMP center dot+)Fe-IV(O)(X-).