Pi Chengfu, Liu Ruiting, Zheng Pengzhi, Chen Zhenxia, Zhou Xigeng
Department of Chemistry, Shanghai Key Laboratory of Molecular Catalysis and Innovative Material, Fudan University, Shanghai 200433, People's Republic of China.
Inorg Chem. 2007 Jun 25;46(13):5252-9. doi: 10.1021/ic070203p. Epub 2007 May 25.
The dinuclear ytterbium pyridyl diamido complexes Cp(2)Yb(THF)[mu-eta(1):eta(2)-(NH)(2)(C(5)H(3)N-2,6)] (1a) and Cp(2)Yb(THF)[mu-eta(1):eta(2)-(NH)(2)(C(5)H(3)N-2,3)] (1b) are easily prepared by protonolysis of Cp(3)Yb 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 (Cp(2)Yb)(2)[mu-eta(2):eta(2)-(CyN(CyNH)CN)(2)(C(5)H(3)N-2,6)] (2) in 42% yield. Compound 2 is unstable to heat and slowly isomerized to the mixed neutral/dianionic diguanidinate complex (Cp(2)Yb)(2)mu-eta(2):eta(2)-(CyNH)(2)CN(C(5)H(3)N-2,6)NC(NCy)(2) (3) at room temperature. Similarly, treatment of 1b with 2 equiv of CyN=C=NCy gives the addition/ isomerization product (Cp(2)Yb)(2)[mu-eta(2):eta(2):eta(1)-(CyNH)(2)CN(C(5)H(3)N-2,3)NC(NCy)(2)] (4). Moreover, the reaction of various ytterbium aryl diamido complexes (prepared in situ from Cp(2)YbMe and aryldiamine, respectively) with CyN=C=NCy affords the corresponding addition products (Cp(2)Yb)(2)[mu-eta(2):eta(2)-{CyN(CyNH)CN}(2)(C(6)H(4)-1,4)] (5), (Cp(2)Yb)(2)mu-eta(2):eta(2)-{CyN(CyNH)CN}(2)(C(6)H(4)-1,3), and (Cp(2)Yb)(2)[mu-eta(2):eta(2)-{CyN(CyNH)CN}(2)(C(13)H(8)-2,7)] (7), respectively. In contrast to pyridyl-bridged bis(guanidinate monoanion) complexes, aryl-bridged bis(guanidinate monoanion) complexes 5-7 are stable even with prolonged heating at 110 degrees 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.
双核镱吡啶二酰胺配合物Cp(2)Yb(THF)[μ-η(1):η(2)-(NH)(2)(C(5)H(3)N-2,6)] (1a)和Cp(2)Yb(THF)[μ-η(1):η(2)-(NH)(2)(C(5)H(3)N-2,3)] (1b)分别通过用0.5当量相应的二氨基吡啶对Cp(3)Yb进行质子解反应，以可接受的产率轻松制备。在低温下，于四氢呋喃中用2当量的二环己基碳二亚胺(CyN=C=NCy)处理1a，可分离得到形式上的双N-H加成产物(Cp(2)Yb)(2)[μ-η(2):η(2)-(CyN(CyNH)CN)(2)(C(5)H(3)N-2,6)] (2)，产率为42%。化合物2对热不稳定，在室温下会缓慢异构化为混合中性/双阴离子双胍配合物(Cp(2)Yb)(2)μ-η(2):η(2)-(CyNH)(2)CN(C(5)H(3)N-2,6)NC(NCy)(2) (3)。类似地，用2当量的CyN=C=NCy处理1b可得到加成/异构化产物(Cp(2)Yb)(2)[μ-η(2):η(2):η(1)-(CyNH)(2)CN(C(5)H(3)N-2,3)NC(NCy)(2)] (4)。此外，各种镱芳基二酰胺配合物(分别由Cp(2)YbMe和芳基二胺原位制备)与CyN=C=NCy反应可得到相应的加成产物(Cp(2)Yb)(2)[μ-η(2):η(2)-{CyN(CyNH)CN}(2)(C(6)H(4)-1,4)] (5)、(Cp(2)Yb)(2)μ-η(2):η(2)-{CyN(CyNH)CN}(2)(C(6)H(4)-1,3)和(Cp(2)Yb)(2)[μ-η(2):η(2)-{CyN(CyNH)CN}(2)(C(13)H(8)-2,7)] (7)。与吡啶桥连的双(胍单阴离子)配合物不同，芳基桥连的双(胍单阴离子)配合物5 - 7即使在110℃下长时间加热也很稳定。所有结果不仅表明吡啶桥的存在可赋予二酰胺配合物独特的反应活性并引发意外的反应序列，而且明显表明双胍配体的负电荷数量和分布可从双单阴离子单元调节为混合中性/双阴离子异构体。所有配合物均通过元素分析和红外光谱进行表征。配合物1a、3、5、6和7的结构也通过X射线单晶衍射分析确定。
