Cyclopentadienyl chromium diimine and pyridine-imine complexes: ligand-based radicals and metal-based redox chemistry
作者:Wen Zhou、Linus Chiang、Brian O. Patrick、Tim Storr、Kevin M. Smith
DOI:10.1039/c2dt30160a
日期:——
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.
制备并表征了具有反铁磁偶联的阴离子自由基二亚胺和吡啶亚胺配体的顺磁性 CpCr(III) 配合物。二亚胺氯 CpCr[(ArNCR)2]Cl 配合物(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)通过对先前报道的 Cr(二亚胺)(THF)2Cl2 前驱体进行 NaCp 处理合成。用 Zn 还原 1 得到 CpCr[(DppNCH)2],4,其源于 Cr(III) 还原为 Cr(II) 并保留了配体基自由基。烷氧化物配合物 CpCr[(DppNCH)2](OCR2R′)(5: R = Me, R′ = Ph; 6: R = iPr, R′ = H)通过中性二亚胺和催化碱存在下 Cp2Cr 与 HOCR2R′ 的质子解反应合成。相应的自由基吡啶亚胺配合物 CpCr(PyCHNMes)Cl (9)、CpCr(PyCHNMes) (8) 和 CpCr(PyCHNMes)(OCMe2Ph) (11) 通过类似方法制备。用碘氧化 8 得到 CpCr(PyCHNMes)I (10),其中 Cr(II) 氧化为 Cr(III) 再次保留了阴离子吡啶亚胺配体。通过单晶 X 射线衍射确定了配合物 1、2、4-8、10 和 11 的分子结构。在报道的配合物的 UV-vis 光谱中观察到异常的低能带,尤其是 Cr(II) 配合物 4 和 8 的强跃迁。通过理论计算研究了吡啶亚胺配合物 8 和 10 的电子结构。