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

• Published in: European Journal of Inorganic Chemistry 2012-01, Vol.2012 (3), p.535-545
• Main Authors: Russell, Sarah K., Bowman, Amanda C., Lobkovsky, Emil, Wieghardt, Karl, Chirik, Paul J.
• Format: Article
• Language: English
• Subjects: Catalysts; Chelates; Manganese; Non-innocent ligands; Redox chemistry
• ISSN: 1434-1948; 1099-0682
• DOI: 10.1002/ejic.201100569

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‐iPr2–C6H3N=CMe)2C5H3N} 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 MnII 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 MnI, 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 MnI, d6 electron configuration imparted by the strong‐field carbonyl ligands. The chemistry of reduced aryl‐substituted bis(imino)pyridine manganese complexes has been explored with the goal of elucidating the role of the redox‐active chelate. The bis(THF) derivative [(iPrPDI)Mn(THF)2] is a high‐spin MnII complex antiferromagnetically coupled to a bis(imino)pyridine diradical, while the related dicarbonyl complex is a low‐spin MnI, d6 derivative with a ligand‐based SOMO.