Activation of C–H, N–H, and O–H Bonds via Proton-Coupled Electron Transfer to a Mn(III) Complex of Redox-Noninnocent Octaazacyclotetradecadiene, a Catenated-Nitrogen Macrocyclic Ligand

• Published in: Journal of the American Chemical Society 2019-04, Vol.141 (14), p.5699-5709
• Main Authors: Vaddypally, Shivaiah, Tomlinson, Warren, O’Sullivan, Owen T, Ding, Ran, Van Vliet, Megan M, Wayland, Bradford B, Hooper, Joseph P, Zdilla, Michael J
• Format: Article
• Language: English
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/jacs.8b10250

Reaction of 1,3-diazidopropane with an electron-rich Mn­(II) precursor results in oxidation of the metal center to a Mn complex with concomitant assembly of the macrocyclic ligand into the 1,2,3,4,­8,9,10,11-octa­aza­cyclo­tetra­deca-2,9-diene-1,4,8,11-tetraido (OIM) ligand. Although describable as a Werner Mn­(V) complex, analysis by X-ray diffraction, magnetic measurements, X-ray photoelectron spectroscopy, cyclic voltammetry, and density functional theory calculations suggest an electronic structure consisting of a Mn­(III) metal center with a noninnocent OIM diradical ligand. The resulting complex, (OIM)­Mn­(NH t Bu), reacts via proton-coupled electron transfer (PCET) with phenols to form phenoxyl radicals, with dihydroanthracene to form anthracene, and with (2,4-ditert-butyltetrazolium-5-yl)­amide to extrude a tetrazyl radical. PCET from the latter generates the isolable corresponding one-electron reduced compound with a neutral, zwitterionic axial 2,4-ditert-butyltetrazolium-5-yl)­amido ligand. Electron paramagnetic resonance and density functional theoretical analyses suggest an electronic structure wherein the manganese atom remains Mn­(III) and the OIM ligand has been reduced by one electron to a monoradical noninnocent ligand. The result indicates PCET processes whereby the proton is transferred to the axial ligand to extrude t BuNH2, the electron is transferred to the equatorial ligand, and the central metal remains relatively unperturbed.