Manganese(III) and rhenium(II) complexes with bulky 4,6-di-tert-butyl-N-(2,6-di-iso-propylphenyl)-o-iminobenzoquinonato ligands via carbonyls of corresponding metals

Four-coordinate complex MnIII(ISQ-Pri)(AP-Pri) (1), where ISQ-Pri = 4,6-di-tert-butyl-N-(2,6-di-iso-propylphenyl)-o-iminobenzosemiquinonate anion-radical, AP-Pri = 4,6-di-tert-butyl-N-(2,6-di-iso-propylphenyl)-o-amidophenolate dianion, has been prepared by the reaction of Mn2(CO)10 with free 4,6-di-tert-butyl-N-(2,6-di-iso-propylphenyl)-o-iminobenzoquinone (IBQ-Pri) in the molar ratio 1:4 in toluene. In contrast to manganese, rhenium carbonyl reacts with o-iminobenzoquinone to form complex ReII(ISQ-Pri)2(CO)2 (2) with the retention of two carbonyls in coordination sphere of rhenium. The complexes have been characterized by IR, UV–Vis, and EPR spectroscopies. Molecular structures of compounds 1 and 2 have been determined by single-crystal X-ray crystallography. Compound 1 is centro-symmetric square-planar molecule with delocalized mixed valent state of AP-Pri and ISQ-Pri ligands. EPR spectrum of 1 in solid at 300–77 K is typical for manganese complexes with S = 3/2 state. The effective magnetic moment of 1 is 1.96 μB at temperature 5 K as it was established by variable-temperature magnetic susceptibility measurements. Six-coordinate octahedral complex 2 possesses an S = 1/2 ground state, which is attained via strong intramolecular antiferromagnetic interaction between t2g orbital unpaired electron of the low spin ReII ion and the unpaired electron on π-orbital of the radical ligand.

Graphical abstractThe interaction of metal carbonyls M2 (CO)10 (M = Mn, Re) with sterically hindered 4,6-di-tert-butyl-N-(2,6-di-iso-propylphenyl)-o-iminobenzoquinone (IBQ-Pri) leads to the formation of unusual four-coordinate bis-o-iminobenzoquinonato complex MnIII(ISQ-Pri)(AP-Pri) of square-planar geometry and hexa-coordinate complex ReII(ISQ-Pri)2 (CO)2. ISQ-Pri and AP-Pri represent anion-radical and dianion of IBQ-Pri. Manganese complex was found to be able to bind dioxygen.Figure optionsDownload full-size imageDownload as PowerPoint slide