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Issue 26, 2012
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Cyclopentadienyl chromium diimine and pyridine-imine complexes: ligand-based radicals and metal-based redox chemistry

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Abstract

Paramagnetic CpCr(III) complexes with antiferromagnetically-coupled anionic radical diimine and pyridine-imine ligands were prepared and characterized. The diimine chloro CpCr[(ArNCR)2]Cl complexes (1: Ar = 2,6-iPr2C6H3 (Dpp), R = H; 2: Ar = 2,6-Me2C6H3 (Xyl), R = Me; 3: Ar = 2,4,6-Me3C6H2 (Mes), R = Me) were synthesized by treatment of previously reported Cr(diimine)(THF)2Cl2 precursors with NaCp. Reduction of 1 with Zn gives CpCr[(DppNCH)2], 4, resulting from reduction of Cr(III) to Cr(II) with retention of the ligand-based radical. Alkoxide complexes CpCr[(DppNCH)2](OCR2R′) (5: R = Me, R′ = Ph; 6: R = iPr, R′ = H) were synthesized by protonolysis of Cp2Cr with HOCR2R′ in the presence of the neutral diimine and catalytic base. The corresponding radical pyridine-imine complexes CpCr(PyCHNMes)Cl (9), CpCr(PyCHNMes) (8), and CpCr(PyCHNMes)(OCMe2Ph) (11), were prepared by analogous routes. Oxidation of 8 with iodine gives CpCr(PyCHNMes)I (10) where oxidation of Cr(II) to Cr(III) again occurs with retention of the anionic pyridine-imine radical ligand. The molecular structures of complexes 1, 2, 4–8, 10 and 11 were determined by single-crystal X-ray diffraction. Unusual low energy bands were observed in the UV-vis spectra of the reported complexes, with particularly strong transitions observed for the Cr(II) complexes 4 and 8. The electronic structure of pyridine-imine complexes 8 and 10 were investigated by theoretical calculations.

Graphical abstract: Cyclopentadienyl chromium diimine and pyridine-imine complexes: ligand-based radicals and metal-based redox chemistry

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Publication details

The article was received on 20 Jan 2012, accepted on 16 Apr 2012 and first published on 19 Apr 2012


Article type: Paper
DOI: 10.1039/C2DT30160A
Citation: Dalton Trans., 2012,41, 7920-7930
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    Cyclopentadienyl chromium diimine and pyridine-imine complexes: ligand-based radicals and metal-based redox chemistry

    W. Zhou, L. Chiang, B. O. Patrick, T. Storr and K. M. Smith, Dalton Trans., 2012, 41, 7920
    DOI: 10.1039/C2DT30160A

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