Lanthanide-Induced Diinsertion of Isocyanates into the N−H Bond: Synthesis, Structure, and Reactivity of Organolanthanides Containing Diureido Ligands

Treatment of [Cp2LnNHPy]2 (Py = 2-pyridyl) (1) with 4-nitrophenyl isocyanate gives the unexpected complexes Cp2Ln[η2:η1-PyNCON(C6H4NO2-4)CONHC6H4NO2-4] (Ln = Yb (5a), Er (5b)) as the main product regardless of the equivalency of isocyanate reagent employed. The more bulky isocyanate (2,6-iPr2C6H3NCO) also undergoes double insertion into 1, affording Cp2Ln[η2:η1-PyNCON(C6H3iPr2-2,6)CONHC6H3iPr2-2,6] (Ln = Yb (6a), Er (6b)). Reaction of 1 with 4 equiv of ClCH2CH2CH2NCO affords Cp2Ln[η2:η1-PyNCON(CH2CH2CH2Cl)CONH(CH2)3Cl] (Ln = Yb (7a), Er (7b)) in good yields. Moreover, [(C5H4Me)2LnNHPy]2 (Ln = Yb (2a), Er (2b), Y (2c)) are also reactive toward isocyanate diinsertion, giving (C5H4Me)2Ln[η2:η1-PyNCON(Ph)CONHPh] (Ln = Yb (8a), Er (8b), Y (8c)) in almost quantitative yields. Furthermore, it is found that the presence of electron-withdrawing and electron-donating substituents on the pyridyl ring does not appear to alter the product selectivity and yields. The diinsertion of PhNCO into [Cp2LnNHPyMe]2 (PyMe = 4-methyl-2-pyridyl) (3) and [Cp2LnNHPyCl]2 (PyCl = 5-chloro-2-pyridyl) (4) leads to the formation of Cp2Ln[η2:η1-PyMeNCON(Ph)CONHPh] (Ln = Er (9a), Y (9b)) and Cp2Ln[η2:η1-PyClNCON(Ph)CONHPh] (Ln = Yb (10a), Er (10b), Y (10c)), respectively. In addition, the monoinsertion intermediate Cp2Yb[η2-N(Py)CONHC6H3iPr2-2,6](HMPA) (11·HMPA) can be trapped during this diinsertion process by adding HMPA. Interestingly, the mixed diinsertion complex Cp2Yb[η2:η1-PyNCON(C6H3iPr2-2,6)CONHPh] (12) can be prepared by allowing 2,6-iPr2C6H3NCO to react first with PyNH2 and then with Cp3Yb followed by inserting with PhNCO or by the reaction of 11 with PhNCO. On the other hand, treatment of 6a with excess PhNCO leads to the replacement of 2,6-iPr2C6H3NCO units inserted into the N−H bond by PhNCO molecules, wherein the newly formed ligand has been structurally characterized in its protonated form PyNHCON(Ph)CONHPh (13). Similarly, PyNHCON(C6H3iPr2-2,6)CONHC6H3iPr2-2,6 (14) could also be obtained by reaction of Cp2Yb[PyNCON(Ph)CONHPh] with excess 2,6-iPr2C6H3NCO followed by hydrolysis. All the complexes were characterized by spectroscopic analysis. The structures of compounds 5−14 are also determined through X-ray single-crystal diffraction analysis.

以 [Cp2LnNHPy]2 (Py = 2-吡啶基) (1) 与 4-硝基苯异氰酸酯的反应，出人意料地生成了主产物 Cp2Ln[η2:η1-PyNCON(C6H4NO2-4)CONHC6H4NO2-4] (Ln = Yb (5a), Er (5b))，无论所使用的异氰酸酯试剂的等当量如何。更庞大的异氰酸酯 (2,6-iPr2C6H3NCO) 也经历了1的双插入反应，生成 Cp2Ln[η2:η1-PyNCON(C6H3iPr2-2,6)CONHC6H3iPr2-2,6] (Ln = Yb (6a), Er (6b))。1与4等当量的 ClCH2CH2CH2NCO 反应，以良好的产率得到 Cp2Ln[η2:η1-PyNCON(CH2CH2CH2Cl)CONH(CH2)3Cl] (Ln = Yb (7a), Er (7b))。此外，[(C5H4Me)2LnNHPy]2 (Ln = Yb (2a), Er (2b), Y (2c)) 对异氰酸酯二插入反应也表现出活性，以几乎定量产率生成 (C5H4Me)2Ln[η2:η1-PyNCON(Ph)CONHPh] (Ln = Yb (8a), Er (8b), Y (8c))。进一步研究发现，吡啶环上吸电子基团和给电子基团的存在似乎不会改变产物的选择性和产率。PhNCO 对 [Cp2LnNHPyMe]2 (PyMe = 4-甲基-2-吡啶基) (3) 和 [Cp2LnNHPyCl]2 (PyCl = 5-氯-2-吡啶基) (4) 的二插入反应，分别导致 Cp2Ln[η2:η1-PyMeNCON(Ph)CONHPh] (Ln = Er (9a), Y (9b)) 和 Cp2Ln[η2:η1-PyClNCON(Ph)CONHPh] (Ln = Yb (10a), Er (10b), Y (10c)) 的形成。此外，在二插入过程中，通过添加 HMPA 可以捕获单插入中间体 Cp2Yb[η2-N(Py)CONHC6H3iPr2-2,6](HMPA) (11·HMPA)。有趣的是，可以通过先让 2,6-iPr2C6H3NCO 与 PyNH2 反应，然后与 Cp3Yb 反应，随后插入 PhNCO，或者通过 11 与 PhNCO 的反应来制备混合二插入复杂物 Cp2Yb[η2:η1-PyNCON(C6H3iPr2-2,6)CONHPh] (12)。另一方面，6a 与过量 PhNCO 的处理导致插入到 N−H 键中的 2,6-iPr2C6H3NCO 单元的替换，新形成的配体以质子化形式 PyNHCON(Ph)CONHPh (13) 进行结构表征。同样，通过 Cp2Yb[PyNCON(Ph)CONHPh] 与过量 2,6-iPr2C6H3NCO 的反应，随后进行水解，也可以获得 PyNHCON(C6H3iPr2-2,6)CONHC6H3iPr2-2,6 (14)。所有这些复杂物均通过光谱分析进行了表征。化合物 5−14 的结构也通过单晶X射线衍射分析确定。