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 [(^iPrPDI)MnCl₂] {^iPrPDI = 2,6-(2,6-iPr ₂-C₆H₃N=CMe)₂C₅H ₃N} with excess Na and catalytic (0.5 mol-%) naphthalene furnished the bis(THF) compound [(^iPrPDI)Mn(THF)₂]. Performing the reduction with excess Na(Hg) in toluene furnished the bis(chelate) manganese compound [(^iPrPDI)₂Mn]. 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 [(^iPrPDI)Mn(CO)₂], a low-spin Mn^I, d⁶ compound with an experimentally observed bis(imino)pyridine-centred radical. Oxidation and reduction of this compound furnished [(^iPrPDI)Mn(CO)₃]⁺ and [( ^iPrPDI)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, d⁶ electron configuration imparted by the strong-field carbonyl ligands.