ic070203p_si_003.cif (130.41 kB)

Selective Reaction Based on the Linked Diamido Ligands of Dinuclear Lanthanide Complexes

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posted on 25.06.2007, 00:00 by Chengfu Pi, Ruiting Liu, Pengzhi Zheng, Zhenxia Chen, Xigeng Zhou
The dinuclear ytterbium pyridyl diamido complexes [Cp2Yb(THF)]2[μ-η12-(NH)2(C5H3N-2,6)] (1a) and [Cp2Yb(THF)]2[μ-η12-(NH)2(C5H3N-2,3)] (1b) are easily prepared by protonolysis of Cp3Yb with 0.5 equiv of the corresponding diaminopyridine in accepted yields, respectively. Treatment of 1a with 2 equiv of dicyclohexylcarbodiimide (CyNCNCy) in THF at low temperature leads to the isolation of the formal double N−H addition product (Cp2Yb)2[μ-η22-(CyN(CyNH)CN)2(C5H3N-2,6)] (2) in 42% yield. Compound 2 is unstable to heat and slowly isomerized to the mixed neutral/dianionic diguanidinate complex (Cp2Yb)2[μ-η22-(CyNH)2CN(C5H3N-2,6)NC(NCy)2](THF) (3) at room temperature. Similarly, treatment of 1b with 2 equiv of CyNCNCy gives the addition/ isomerization product (Cp2Yb)2[μ-η221-(CyNH)2CN(C5H3N-2,3)NC(NCy)2] (4). Moreover, the reaction of various ytterbium aryl diamido complexes (prepared in situ from [Cp2YbMe]2 and aryldiamine, respectively) with CyNCNCy affords the corresponding addition products (Cp2Yb)2[μ-η22-{CyN(CyNH)CN}2(C6H4-1,4)] (5), (Cp2Yb)2[μ-η22-{CyN(CyNH)CN}2(C6H4-1,3)](6), and (Cp2Yb)2[μ-η22-{CyN(CyNH)CN}2(C13H8-2,7)] (7), respectively. In contrast to pyridyl-bridged bis(guanidinate monoanion) complexes, aryl-bridged bis(guanidinate monoanion) complexes 57 are stable even with prolonged heating at 110 °C. All the results not only demonstrate that the presence of the pyridyl bridge can impart the diamido complexes with a unique reactivity and initiate the unexpected reaction sequence but also indicate evidently that the number and distribution of negative charges of the diguanidinate ligand is tunable from double monoanionic units to mixed neutral/dianionic isomers. All the complexes are characterized by elemental analysis and IR spectroscopies. The structures of complexes 1a, 3, 5, 6, and 7 are also determined through X-ray single-crystal diffraction analysis.