A side-on Mn(iii)–peroxo supported by a non-heme pentadentate N3Py2 ligand: synthesis, characterization and reactivity studies

Abstract

A mononuclear manganese(III)–peroxo complex [Mn^III(N₃Py₂)(O₂)]⁺ (1a) bearing a non-heme N,N′-dimethyl-N-(2-(methyl(pyridin-2-ylmethyl)amino)ethyl)-N′-(pyridin-2-ylmethyl)ethane-1,2-diamine (N₃Py₂) ligand was synthesized by the reaction of [Mn(N₃Py₂)(H₂O)](ClO₄)₂ (1) with hydrogen peroxide and triethylamine in CH₃CN at 25 °C. The reactivity of 1a in aldehyde deformylation using 2-phenyl propionaldehyde (2-PPA) was studied and the reaction kinetics was monitored by UV-visible spectroscopy. A kinetic isotope effect (KIE) = 1.7 was obtained in the reaction of 1a with 2-PPA and α-[D₁]-PPA, suggesting nucleophilic character of 1a. The activation parameters ΔH^‡ and ΔS^‡ were determined using the Eyring plot while E_a was obtained from the Arrhenius equation by performing the reaction between 288 and 303 K. Hammett constants (σ_p) of para-substituted benzaldehydes p-X-Ph-CHO (X = Cl, F, H, and Me) were linear with a slope (ρ) = 3.0. Computational study suggested that the side-on structure of 1a is more favored over the end-on structure and facilitates the reactivity of 1a.