. Quaternization by radical additions, e.g. MHAT alkene hydrofunctionalization rapid MHAT with alkenes, in which its formation-not its consumption-is rate limiting and its instability drives reaction with even hindered alkenes. The iron porphyrin, in turn, has been proposed to form reactive alkyliron complexes 12 subject to SH2 by alkyl radicals. The Fe(acac)3 catalyst, however, required an air atmosphere to turn over the Fe 2+ intermediate, a common problem in MHAT (see below). We wondered if Fe(TPP)Cl itself might form an iron hydride that could undergo MHAT 15 with more reactive alkenes, but turn over by engagement of the benzyl halide coupling partner 16 (Figure ) instead of O2. 17 Styrenes were chosen as test substrates because their resulting benzyl radicals might be formed by MHAT from reasonably stable Fe-H bonds. This design, however, involved the intermediacy of two semi-persistent radicals that might lead to uncontrolled homo-coupling and statistical mixtures (see below).