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Equatorial Ligand Perturbations Influence the Reactivity of Manganese(IV)‐Oxo Complexes
Author(s) -
Massie Allyssa A.,
Denler Melissa C.,
Cardoso Luísa Thiara,
Walker Ashlie N.,
Hossain M. Kamal,
Day Victor W.,
Nordlander Ebbe,
Jackson Timothy A.
Publication year - 2017
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.201612309
Subject(s) - chemistry , reactivity (psychology) , manganese , ligand (biochemistry) , excited state , electron transfer , crystallography , electron paramagnetic resonance , photochemistry , hydrogen atom , redox , oxidation state , catalysis , inorganic chemistry , nuclear magnetic resonance , organic chemistry , atomic physics , medicine , biochemistry , receptor , alkyl , pathology , physics , alternative medicine
Manganese(IV)‐oxo complexes are often invoked as intermediates in Mn‐catalyzed C−H bond activation reactions. While many synthetic Mn IV ‐oxo species are mild oxidants, other members of this class can attack strong C−H bonds. The basis for these reactivity differences is not well understood. Here we describe a series of Mn IV ‐oxo complexes with N5 pentadentate ligands that modulate the equatorial ligand field of the Mn IV center, as assessed by electronic absorption, electron paramagnetic resonance, and Mn K‐edge X‐ray absorption methods. Kinetic experiments show dramatic rate variations in hydrogen‐atom and oxygen‐atom transfer reactions, with faster rates corresponding to weaker equatorial ligand fields. For these Mn IV ‐oxo complexes, the rate enhancements are correlated with both 1) the energy of a low‐lying 4 E excited state, which has been postulated to be involved in a two‐state reactivity model, and 2) the Mn III/IV reduction potentials.