The report of the first crystal structure of an oxoiron(IV) complex [FeIV(Oanti)(TMC)(CH3CN)]2+ (TMC = tetramethylcyclam) in 2003 has stimulated the synthesis and characterization of a number of high-valent oxoiron complexes and the investigation of their H-atom transfer (HAT) and O-atom transfer (OAT) reactivities. This poster will compare reactivity differences between the syn and anti-isomers of oxoiron(IV) species supported by the same tetramethylcyclam (TMC) ligand, which differ only in the orientations of the oxo moiety relative to its four methyl groups that occupy the same face of the macrocycle. Interestingly, HAT rates of the two isomers in the oxidation of 1,4-cyclohexadiene at 293 K only differ by a factor of 2. However, there is a much larger difference with respect to OAT reactions. The reactions of the syn-isomer with OAT substrates, thioanisole (PhSMe) and triphenylphosphene (Ph3P), exhibit second order rate constants of ~12 M-1s-1 at 298 K and ~13 M-1s-1 at 233 K, which are around 800- and 3000-fold faster than found for its anti-isomer. It is conjectured that the affinity of the trans ligand, either the triflate counterion or the solvent MeCN, for the Fe=O unit may dictate the OAT reactivity, which may be probed by monitoring the 19F NMR signals of the triflate counterion. The results of this investigation will be presented.

Insights into HAT and OAT reactivity differences between syn and anti Isomers of [FeIV(O)TMC]2+

ACS Spring 2022

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