Structural Characterization and Remarkable Axial Ligand Effect on the Nucleophilic Reactivity of a Nonheme Manganese(III)–Peroxo Complex

Abstract

The dark side of the Mn: A manganese(III) complex bearing a 13-membered macrocyclic ligand (1, see picture) binds a peroxo ligand in a side-on eta(2) fashion. The reactivity of 1 is influenced by the introduction of anionic ligands trans to the peroxo group. Electronic and structural changes upon trans-ligand binding explain the increased nucleophilicity of the resulting complexes 1-X.

Transition Metal Complexes and the Activation of Dioxygen

“…A role of the axial ligand has been proposed to be to enhance the nucleophilicity of the O 2 À 2 moiety. This has been recently demonstrated for a non-heme Mn(III)-peroxo complex, for which the authors postulate the axial ligand to facilitate the conversion between the η 2 and η 1 conformations [60]. It was also shown for the 2 )] (tpp ¼ 5,10,15,20-tetrakis-(pentafluorophenyl)porphyrin) that epoxidation of the olefin 2-methyl-1,4-naphthoquinone only proceeds in the presence of 20 % dimethyl sulfoxide, which the authors attributed to increased axial coordination at the Fe(III) center [61].…”

Geometric and electronic structure of a peroxomanganese(iii) complex supported by a scorpionate ligand

“…In contrast, a variety of synthetic peroxomanganese(III) species have been generated and characterized, offering insights into the structural, electronic, and reactivity properties of this class of compound. 14–27 Members of this class of compound include side-on peroxomanganese(III) adducts (Mn III -O 2 ) and end-on alkylperoxomanganese(III) adducts (Mn III -OOR). 28,29 …”

“…While there are several examples of Mn III -O 2 complexes with anionic supporting ligands, 14,22,25,30 there are no detailed bonding descriptions of such complexes. As many enzymatic Mn III -O 2 adducts are expected to feature anionic ligands, this represents a gap in knowledge.…”

“…23 In contrast, crystallographically-characterized mononuclear Mn III -O 2 adducts supported by tetramethylcylam (TMC) and its derivatives (Scheme 1) show τ parameters from 0 to 0.52, with the variation reflecting the size of the macrocyclic ring. 14,21,24 …”

Chapter 1. Experimental and Computational Studies on the Catalytic Mechanism of Non-heme Iron Dioxygenases

“…146 Interestingly, molecular oxygen binds in a side-on fashion rather than end-on in the structure shown in Figure 1.20, which contrasts an end-on bound NO crystal structure as well as biomimetic dioxygen bound structures. 147,148 Addition of hydrogen peroxide to the oxygenase domain led to cis-hydroxylation products efficiently without the need for additional electrons. 149 Moreover, use of H 2 18 O 2 led to isotopically labeled products indicating that both oxygen atoms in the product originate from hydrogen peroxide.…”