Synthesis and Electronic Structure of Reduced Bis(imino)pyridine Manganese Compounds

The synthesis and electronic structure of reduced aryl-substituted bis(imino) pyridine manganese compounds have been explored. Stirring a THF slurry of [((PDI)-P-iPr)MnCl2] {(PDI)-P-iPr = 2,6-(2,6-iPr(2)-C6H3N=CMe)(2)C5H3N} with excess Na and catalytic (0.5 mol-%) naphthalene furnished the bis(THF) compound [((PDI)-P-iPr)Mn(THF)(2)]. Performing the reduction with excess Na(Hg) in toluene furnished the bis(chelate) manganese compound [((PDI)-P-iPr)(2)Mn]. For both compounds, a combination of EPR spectroscopy, magnetic measurements and metrical parameters determined from X-ray diffraction established high-spin Mn-II compounds with reduced, redox-active bis( imino) pyridine ligands. Substitution of the THF ligands with carbon monoxide yielded [((PDI)-P-iPr)Mn(CO)(2)], a low-spin Mn-I, d(6) compound with an experimentally observed bis(imino)pyridine-centred radical. Oxidation and reduction of this compound furnished [((PDI)-P-iPr)Mn(CO)(3)](+) and [((PDI)-P-iPr)Mn(CO)(2)](-), respectively, and provided a series of three manganese carbonyl compounds over three oxidation states. Elucidation of the electronic structure of these compounds established that oxidation events within the series are ligand-rather than manganese-based, most likely a result of the stable low-spin Mn-I, d(6) electron configuration imparted by the strong-field carbonyl ligands.